An aquaculture organism floc and microbial fuel cell coupling system and method

Abstract

This invention provides a coupling system and method for aquaculture bioflocs and microbial fuel cells, comprising an aquaculture reactor body filled with aquaculture water containing bioflocs, and a microbial fuel cell assembly and an aeration device. The microbial fuel cell assembly includes an anode, a cathode, and an external circuit, with the external circuit connecting the anode and cathode. The aeration device includes an aeration head and an oxygen pump, with the oxygen pump connected to the aeration head via an air pipe to provide compressed air to the aeration head. The aeration head is suspended directly above the anode with upward air output, creating a relatively anaerobic environment for the anode and an oxygen-rich environment for the cathode. This invention achieves in-situ zero-emission purification of the aquaculture water, simultaneously supplying BFT biological metabolism, "activating" MFC for electricity generation, and then using microcurrent excitation to enhance denitrification. The system has a simple structure, low operating cost, and high stability, making it suitable for small and medium-sized aquaculture farms.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture and water environment engineering technology, and particularly relates to a coupling system and method for aquaculture bioflocs and microbial fuel cells. Background Technology

[0002] As aquaculture develops towards high density and intensification, the problem of pollutant accumulation in aquaculture water bodies is becoming increasingly prominent. Pollutants such as ammonia nitrogen, nitrite nitrogen, and total organic carbon not only affect the growth and survival of farmed animals, but also cause environmental pollution in aquaculture wastewater. Therefore, efficient purification of aquaculture water bodies has become the key to the sustainable development of aquaculture.

[0003] Currently, wastewater treatment technologies for aquaculture systems mainly include physical, biological, and electrochemical methods. Traditional biological treatment methods suffer from high sludge production and energy consumption, while emerging electrochemical treatment technologies face drawbacks such as high cost and easy generation of byproducts. From the perspective of system operation, the pH and temperature of the aquaculture water can easily affect microbial activity, and reactors are prone to clogging and biofilm shedding, so operational stability needs to be improved. At the same time, existing treatment equipment has high initial investment and high energy consumption, making it difficult for small and medium-sized aquaculture farms to accept it. Moreover, most technologies lack sufficient integration and cannot meet the differentiated needs of different aquaculture species.

[0004] Biofloc Technology (BFT) is a novel aquaculture technology based on microbial community regulation. It regulates the C / N ratio of aquaculture water by adding organic carbon sources and uses the biochemical reactions of heterotrophic bacteria, nitrifying bacteria, and other microorganisms to remove toxic substances such as ammonia nitrogen and nitrite nitrogen, achieving in-situ water purification and feed reuse. It has the advantages of being eco-friendly and water-saving. However, when this technology is used alone, it has problems such as carbon source waste, poor system stability, and high turbidity of aquaculture water. Excessive bioflocs can also easily cause gill blockage in farmed animals.

[0005] Microbial fuel cell (MFC) technology is an innovative bioelectrochemical technology that can convert organic matter and nitrogenous pollutants in wastewater into electrical energy through microbial metabolism. It has the dual functions of water purification and energy recovery and shows good application prospects in aquaculture. However, when used alone, it has limitations such as low power output and insufficient system stability.

[0006] In existing research, BFT and MFC technologies are mostly applied individually in aquaculture, lacking the design of aquaculture systems that couple the two technologies, thus failing to achieve the complementary advantages between the technologies. Therefore, developing a new aquaculture system that combines BFT and MFC technologies to overcome the shortcomings of single technologies and achieve efficient purification of aquaculture water, energy recovery, and stable system operation has become an urgent need to adapt to the green transformation of aquaculture. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a coupling system and method for aquaculture bioflocs and microbial fuel cells. This system, through the coupling of BFT and MFC technologies, utilizes BFT to provide a continuous and stable organic substrate for the MFC, while simultaneously using the electrical energy generated by the MFC to suppress excessive floc growth, achieving in-situ zero-emission purification of the aquaculture water. This effectively solves the problems of carbon source waste and high turbidity associated with BFT alone, as well as the low power output and poor stability of MFC alone. The system of this invention has a simple structure, low operating cost, and high stability, making it suitable for small and medium-sized aquaculture farms.

[0008] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0009] A coupling system for aquaculture bioflocs and microbial fuel cells includes an aquaculture reactor body filled with aquaculture water containing bioflocs, and a microbial fuel cell assembly and an aeration device. The microbial fuel cell assembly includes an anode, a cathode, and an external circuit. The anode is located at the bottom of the reactor body, the cathode is located at the top of the reactor body, and the external circuit connects the anode and the cathode. The aeration device includes an aeration head and an oxygen pump. The oxygen pump is connected to the aeration head through an air pipe to provide compressed air to the aeration head. The aeration head is suspended directly above the anode with the air outlet pointing upwards. The upward aeration creates a relatively anaerobic environment for the anode and an oxygen-rich environment for the cathode.

[0010] In the above scheme, the main body of the aquaculture reactor is an acrylic cylindrical structure.

[0011] In the above scheme, the external circuit includes an adjustable resistance box, an ammeter, and a digital multimeter; the adjustable resistance box and the ammeter are connected in series and then connected to the circuit between the anode and the cathode, and the digital multimeter is connected in parallel across the adjustable resistance box; the anode and the cathode are connected by a copper-plated nickel wire through the external circuit.

[0012] Both the anode and cathode use carbon felt as the electrode material, and the electrode dimensions are: length 10~20 cm, width 10~20 cm, thickness 0.5~2 cm, and the distance between the anode and cathode is 20~40 cm. Furthermore, the microbial fuel cell assembly does not have a proton exchange membrane.

[0013] In the above scheme, the aeration device is an adjustable aeration head.

[0014] In the above scheme, the reactor body is externally connected to a power generation performance monitoring device, which is connected to the external circuit of the microbial fuel cell assembly and is used to collect and record the output voltage and current in real time.

[0015] The formula for calculating the surface current density detected by the power generation performance monitoring device is as follows:

[0016] ,

[0017] The formula for calculating surface power density is:

[0018] ,

[0019] Where U is the output voltage, R is the external circuit resistance, and A is the anode surface area.

[0020] An operation method based on the aquaculture biofloc and microbial fuel cell coupling system includes the following steps:

[0021] Step S1: Add aquaculture water containing bioflocs into the main body of the aquaculture reactor, control the aquaculture density, feed the aquaculture animals according to the proportion of their body weight, and maintain the carbon-nitrogen ratio of the water by supplementing carbon sources.

[0022] Step S2: Turn on the aeration head to aerate upwards at the preset aeration rate, so that the anode area is in a relatively anaerobic environment and the cathode area is in an oxygen-rich environment.

[0023] Step S3: Adjust the adjustable resistor box of the external circuit to the preset resistance value and record the output voltage and current in real time; when measuring the polarization curve and power density curve, adjust the resistor box to different resistance values ​​and collect the corresponding voltage and current values.

[0024] Step S4: Regularly monitor dissolved oxygen, pH, temperature, and the content of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total nitrogen, total organic carbon, total suspended solids, and floc volume in the aquaculture water.

[0025] In the above scheme, the aquaculture density is 1.5-2.5 kg / m³, the aquaculture feed is fed at 2-5% of the weight of the farmed animals, and the carbon-nitrogen ratio of the water is 10-20;

[0026] The aeration rate is 25-50 L / min, so that the dissolved oxygen concentration in the anode region is <2 mg / L and the dissolved oxygen concentration in the cathode region is >5 mg / L;

[0027] The adjustable resistance box of the external circuit is adjusted to 500-1000 Ω during normal operation and to 10-9999 Ω when measuring polarization curves and power density curves.

[0028] Dissolved oxygen, pH, and temperature are measured daily; ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total nitrogen, and total organic carbon content are measured every 1-3 days; and total suspended solids and floc volume are measured every 10-15 days.

[0029] The carbon source is an organic carbon source;

[0030] The aquaculture feed is an extruded compound feed for aquaculture with a crude protein content of ≥31%.

[0031] In the above scheme, the method for cultivating the bioflocs is as follows:

[0032] Brown sugar and a compound bacterial agent including Bacillus subtilis were inoculated into the water. The temperature was controlled at >10℃, dissolved oxygen at >5mg / L, and the carbon-nitrogen ratio was maintained at 10-20. After 15 days of cultivation, bioflocs with an initial total suspended solids concentration of 7-9 mg / L were obtained.

[0033] In the above scheme, the carbon felt electrodes of the anode and cathode undergo pretreatment before use:

[0034] The carbon felt was soaked in anhydrous ethanol for 30 min and rinsed with deionized water; then it was treated in 0.1 mol / L hydrochloric acid solution at 80-100℃ for 30 min, rinsed with deionized water until neutral, and dried at 80℃ for 24 h; finally, it was soaked in biofloc for 48 h for microbial enrichment.

[0035] In the above scheme, flocculation and precipitation are used to remove color interference from flocs before detecting the content of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. This invention achieves complementary advantages by coupling BFT and MFC technologies. MFC can utilize unused carbon sources and incompletely decomposed feed residues from BFT as substrates to generate stable electricity. Simultaneously, the electrodes of MFC provide attachment sites for microorganisms. Furthermore, the electrical energy generated by MFC can stimulate the activity of related microorganisms in BFT and inhibit excessive growth of biofloc volume, reducing turbidity in aquaculture water and preventing gill blockage in farmed animals, thus solving the problems of carbon source waste and high turbidity associated with BFT technology alone. BFT provides a stable microbial community and substrate for MFC, improving the power output and operational stability of MFC, thus solving the problems of low power and poor stability associated with MFC technology alone.

[0037] 2. This invention achieves in-situ zero-discharge purification of aquaculture water. During operation, only water lost through sampling and natural evaporation is replenished, significantly saving water resources. It can effectively remove pollutants such as ammonia nitrogen, nitrite nitrogen, TN, and TOC. The ammonia nitrogen concentration can be stably controlled below 0.20 mg / L, nitrate nitrogen can be reduced to 0 mg / L, and the TN and TOC contents are significantly lower than those of a single BFT system, demonstrating excellent purification effect.

[0038] 3. The coupling system of the present invention has the dual functions of water purification and energy recovery. The maximum output voltage of the MFC component can reach 295.9mV and the maximum areal power density can reach 1716.8mW / m². It also has good self-recovery capability within the daily cycle. The voltage and power density drop after feeding can be quickly recovered, and the system has strong operational stability.

[0039] 4. The system structure of the present invention is simple, with low initial investment and low operating cost. It does not require complex wastewater treatment equipment, is suitable for the breeding needs of small and medium-sized aquaculture farms, and the breeding reactor is made of acrylic material, which has good light transmittance and corrosion resistance. The external circuit uses copper-plated nickel wire, which has both corrosion resistance and conductivity, and the system is easy to maintain.

[0040] 5. The system operating parameters of this invention are easily adjustable, and the C / N ratio of the water body can be maintained by precisely supplementing the carbon source through the aeration device.

[0041] By adjusting dissolved oxygen levels and regulating the electrical performance of the MFC through an adjustable resistance box, it can be adapted to various high-density aquaculture species such as tilapia, with a stocking density of up to 2.5 kg / m³, achieving intensive aquaculture while ensuring the stability of the aquaculture water. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the BFT-MFC coupled novel aquaculture system in Embodiment 1 of the present invention;

[0043] Figure 2 This is a schematic diagram of the structure of the control group single BFT culture system of the present invention;

[0044] Figure 3 This is the change curve of DO in the aquaculture water in Example 3 of the present invention;

[0045] Figure 4 This is the temperature change curve of the aquaculture water in Example 3 of the present invention;

[0046] Figure 5 This is the pH change curve of the aquaculture water in Example 3 of the present invention;

[0047] Figure 6 This is the daily DO variation curve of the aquaculture water in Example 3 of the present invention;

[0048] Figure 7 This is a daily pH change curve of the aquaculture water in Example 3 of the present invention;

[0049] Figure 8 This is a curve showing the change in ammonia nitrogen content in the aquaculture water in Example 3 of the present invention;

[0050] Figure 9 This is a curve showing the change in nitrite nitrogen content in the aquaculture water in Example 3 of the present invention;

[0051] Figure 10 This is a curve showing the change in nitrate nitrogen content in the aquaculture water in Example 3 of the present invention;

[0052] Figure 11 This is a curve showing the change in total nitrogen content in the aquaculture water in Example 3 of the present invention;

[0053] Figure 12 This is a curve showing the change in total organic carbon content in the aquaculture water in Example 3 of the present invention;

[0054] Figure 13 This is a curve showing the change in floc volume in the aquaculture water in Example 3 of the present invention;

[0055] Figure 14 The output voltage variation curve of the MFC component in Embodiment 3 of the present invention;

[0056] Figure 15 The power density variation curve of the MFC component in Embodiment 3 of the present invention;

[0057] Figure 16 The polarization curve and power density curve of the MFC component in Embodiment 3 of the present invention are shown.

[0058] Figure 17 This is the daily output voltage variation curve of the MFC component in Embodiment 3 of the present invention;

[0059] Figure 18 This is the daily power density variation curve of the MFC component in Embodiment 3 of the present invention;

[0060] In the diagram: 1. Adjustable resistance box; 2. Ammeter; 3. Nickel-plated copper wire; 4. Biofloc; 5. Cathode; 6. Anode; 7. Aeration head; 8. Oxygen pump. Detailed Implementation

[0061] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0062] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "front," "rear," "left," "right," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0063] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0064] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0065] A coupling system of aquaculture bioflocs and microbial fuel cells, such as Figure 1 As shown, the reactor includes a main body filled with aquaculture water containing bioflocs 4, and also includes a microbial fuel cell assembly and an aeration device. The microbial fuel cell assembly includes an anode 6, a cathode 5, and an external circuit. The anode 6 is located at the bottom of the reactor body, the cathode 5 is located at the top of the reactor body, and the external circuit connects the anode 6 and the cathode 5. The aeration device includes an aeration head 7 and an oxygen pump 8. The oxygen pump 8 is connected to the aeration head 7 through an air pipe to provide compressed air to the aeration head 7. The aeration head 7 is suspended directly above the anode 6 with the air outlet direction upward. The upward aeration creates a relatively anaerobic environment for the anode 6 and an oxygen-rich environment for the cathode 5.

[0066] The biofloc 4 was independently cultivated in the laboratory. The cultivation method of the biofloc 4 is as follows: brown sugar and a compound bacterial agent including Bacillus subtilis are inoculated into the water. The temperature is controlled to be >10℃ and the dissolved oxygen is >5 mg / L. Carbon and nitrogen sources are supplemented on time. The carbon source is glucose and the nitrogen source is feed. The carbon-nitrogen ratio is maintained at 10-20 to provide suitable living conditions for the microorganisms in the floc. After 15 days of cultivation, a relatively stable biofloc is obtained. The initial total suspended solids concentration of biofloc 4 is 7-9 mg / L.

[0067] The main body of the aquaculture reactor is an acrylic cylindrical structure. Acrylic material combines light transmission and corrosion resistance, making it suitable for the environmental requirements of aquaculture. The cylindrical structure can reduce stagnant water areas and ensure the uniformity of microbial reactions.

[0068] The external circuit includes an adjustable resistance box 1, an ammeter 2, and a digital multimeter; the adjustable resistance box 1 and the ammeter 2 are connected in series and then connected to the circuit between the anode 6 and the cathode 5, and the digital multimeter is connected in parallel across the adjustable resistance box 1.

[0069] Both the anode 6 and the cathode 5 use carbon felt as the electrode material. The electrode dimensions are: length 10~20 cm, width 10~20 cm, thickness 0.5~2 cm, and the distance between the anode and cathode is 20~40 cm. Furthermore, no proton exchange membrane is provided in the microbial fuel cell assembly.

[0070] The adjustable resistance box 1 has an adjustment range of 10Ω to 9999Ω. During normal operation, the resistance value is set to 500 to 1000Ω. When measuring polarization curves and power density curves, the resistance value can be adjusted as needed.

[0071] The anode 6 and cathode 5 are connected by an external circuit using a copper-plated nickel wire 3. Compared to pure titanium wires, the copper-plated nickel wire 3 has better corrosion resistance and conductivity, ensuring the stable operation of the MFC component.

[0072] The electrical performance monitoring device is connected to the external circuit of the MFC component for real-time acquisition and recording of the MFC's output voltage and current, and can also plot polarization curves and power density curves. The core indicators detected by the electrical performance monitoring device are areal current density and areal power density. The formula for calculating areal current density is: The formula for calculating area power density is: ,in The output voltage (V) of MFC. The resistance of the external circuit is (Ω). The surface area of ​​the anode is (m²).

[0073] The aeration head 7 is an adjustable aeration head, which can control the dissolved oxygen level of the aquaculture water by adjusting the aeration volume, ensuring a relatively anaerobic environment at the anode and an oxygen-rich environment at the cathode, and meeting the dissolved oxygen requirements of microbial oxidation-reduction reactions.

[0074] An operation method based on the aquaculture biofloc and microbial fuel cell coupling system includes the following steps:

[0075] Step S1: Add aquaculture water containing bioflocs 4 into the main body of the aquaculture reactor, control the aquaculture density, feed the aquaculture animals according to the proportion of their body weight, and maintain the carbon-nitrogen ratio of the water by supplementing carbon sources.

[0076] Step S2: Turn on the aeration head 7 to aerate upwards at the preset aeration rate, so that the anode 6 area is in a relatively anaerobic environment and the cathode 5 area is in an oxygen-rich environment.

[0077] Step S3: Adjust the adjustable resistor box 1 of the external circuit to the preset resistance value and record the output voltage and current in real time; when measuring the polarization curve and power density curve, adjust the resistor box to different resistance values ​​and collect the corresponding voltage and current values.

[0078] Step S4: Regularly monitor dissolved oxygen, pH, temperature, and the content of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total nitrogen, total organic carbon, total suspended solids, and floc volume in the aquaculture water.

[0079] Specifically, it includes the following steps:

[0080] Step S1: Add aquaculture water containing bioflocs 4 into the main body of the aquaculture reactor, control the aquaculture density to 1.5-2.5 kg / m³, and feed the aquaculture animals at a ratio of 2-5% of their body weight; at the same time, supplement the carbon source by adding glucose to maintain the C / N ratio of the water at 10-20.

[0081] Step S2: Turn on the aeration device with the single-sided aeration head facing upwards. Set the aeration rate to 25-50 L / min. Since the anode is placed below the single-sided aeration head and the aeration head faces upwards, a relatively anaerobic environment is created for the anode and an oxygen-rich environment is created for the cathode. Specifically, the dissolved oxygen concentration in anode region 6 is <2 mg / L and the dissolved oxygen concentration in cathode region 5 is >5 mg / L. This ensures that the oxidation-reduction reaction of microorganisms in the MFC component proceeds smoothly and provides suitable dissolved oxygen conditions for microorganisms in the biofloc.

[0082] Step S3: Adjust the adjustable resistor box 1 of the external circuit of the MFC component to a suitable resistance value of 500~1000Ω, and record the output voltage and current in real time through the power generation performance monitoring device; when it is necessary to measure the polarization curve and power density curve, adjust the resistance value of resistor box 1 to 10Ω~9999Ω, collect the voltage and current values ​​under different resistances, plot the curves and calculate the maximum surface power density.

[0083] Step S4: Detect the DO, pH, and temperature of the aquaculture water using a water quality monitoring device. Detect the ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen content in the water every 1-3 days. Detect the total suspended solids (TSS) and floc volume every 5-15 days using a biofloc characterization device to keep track of the system's operating status.

[0084] During operation, the aquaculture water body is not replaced; only the water lost due to sampling and natural evaporation is replenished, achieving zero-discharge operation of the aquaculture system and significantly saving water resources.

[0085] Example 1

[0086] A coupling system of aquaculture bioflocs and microbial fuel cells, such as Figure 1 As shown, it includes the main body of the aquaculture reactor, microbial fuel cell (MFC) components, aeration device, and power generation performance monitoring device, with the specific structure as follows:

[0087] The main body of the aquaculture reactor is made of acrylic cylindrical structure with a diameter of 400mm, a height of 300mm, a wall thickness of 5mm, a total volume of 37.68L, and an effective aquaculture volume of 30L.

[0088] Tilapia aquaculture water containing biofloc 4 was added to the reactor. Biofloc 4 is a mature floc specifically for aquaculture. The initial TSS concentration was controlled within an appropriate range.

[0089] Biofloc 4 was independently cultivated in the laboratory. The cultivation method was as follows: an appropriate amount of brown sugar and a compound bacterial agent including Bacillus subtilis were inoculated into the water. The temperature was controlled to be >10℃ and the dissolved oxygen to be >5 mg / L. Carbon and nitrogen sources (glucose as carbon source and feed as nitrogen source) were added on time, and the carbon-nitrogen ratio was maintained at 15 to provide suitable living conditions for the microorganisms in the floc. After about 15 days of cultivation, relatively stable biofloc 4 was obtained, with an initial total suspended solids (TSS) concentration of 7-9 mg / L.

[0090] The MFC module consists of an anode 6, a cathode 5, and an external circuit. The anode 6 is located at the bottom of the reactor body, and the cathode 5 is located at the top. Both the anode 6 and cathode 5 use carbon felt as the electrode material, with electrode dimensions of 15cm × 15cm × 1cm (matching the 30L reactor volume, ensuring sufficient reaction area). The distance between the anode and cathode is 20cm (combined with the unidirectional upward aeration design, it maintains a stable anaerobic environment (DO < 2mg / L) in the anode zone and an oxygen-rich environment (DO > 5mg / L) in the cathode zone, providing an ideal dissolved oxygen gradient for efficient MFC power generation and ensuring unimpeded proton and electron exchange between the anode and cathode). Furthermore, the MFC module does not include a proton exchange membrane (significantly reducing system costs and avoiding membrane fouling and clogging issues, thus improving output power density). The external circuit includes an adjustable resistance box 1, an ammeter 2, and a digital multimeter. The adjustable resistance box 1 has an adjustment range of 10Ω to 9999Ω. During normal operation, the resistance value is set to 1000Ω. The resistance value can be adjusted as needed when measuring polarization curves and power density curves. The anode 6 and cathode 5 are connected by a copper-plated nickel wire 3. The copper-plated nickel wire combines corrosion resistance and conductivity, ensuring the stable operation of the MFC component.

[0091] The electrode underwent pretreatment as follows: An appropriate amount of anhydrous ethanol (enough to ensure sufficient immersion of the electrode material) was added to a beaker, and the cut carbon felt was soaked for 30 minutes with continuous stirring. After treatment, it was rinsed several times with deionized water. The carbon felt was then immersed in an appropriate amount of 0.1 mol / L hydrochloric acid solution and treated at 100℃ for 30 minutes with continuous stirring to remove surface impurities. The treated carbon felt was rinsed several times with deionized water until the surface was neutral and dried in an oven at 80℃ for 24 hours for later use. The pretreatment of the carbon felt primarily aimed to improve its electrochemical activity, increase its effective surface area, and enhance its ability to adsorb electrochemically active substances. After immersing the pretreated graphite carbon felt in inoculated flocs for 48 hours to enrich microorganisms, the microbial-infused carbon felt was assembled into an MFC.

[0092] Aeration device: includes an aeration head 7 and an oxygen pump 8. The aeration head 7 is a single-sided aeration head, suspended directly above the anode 6 with the air outlet direction upward; the oxygen pump 8 is connected to the aeration head 7 via an air pipe, providing compressed air to the aeration head 7. The aeration rate can be controlled by adjusting the output power of the oxygen pump 8, thereby regulating the dissolved oxygen level of the aquaculture water. Upward aeration creates a relatively anaerobic environment (DO < 2 mg / L) for the anode 6, while simultaneously creating an oxygen-rich environment (DO > 5 mg / L) for the cathode 5, meeting the dissolved oxygen requirements of microbial oxidation-reduction reactions.

[0093] Power generation performance monitoring device: The reactor body is externally connected to a power generation performance monitoring device, which is connected to the external circuit of the microbial fuel cell assembly. This device is used to collect and record the output voltage and current in real time, and can plot polarization curves and power density curves. The core indicators detected by the power generation performance monitoring device are surface current density and surface power density.

[0094] The formula for calculating the surface current density detected by the power generation performance monitoring device is as follows:

[0095] ,

[0096] The formula for calculating surface power density is:

[0097] ,

[0098] Where U is the MFC output voltage (V), R is the external circuit resistance (Ω), and A is the anode surface area (m²). In routine experiments, the external circuit resistance R is set to 1000Ω, and the anode surface area A is 0.051m². 3 (The entire surface area of ​​anode 6).

[0099] Example 2

[0100] The high-density tilapia culture was carried out using the aquaculture biofloc and microbial fuel cell coupling system described in Example 1. The specific operation steps are as follows:

[0101] Stocking density and feeding: Aquaculture water containing bioflocs 4 was added to the main body of the aquaculture reactor to simulate a tilapia stocking density of 2 kg / m³. Tongwei aquatic extruded compound feed (crude protein ≥31%; crude fiber ≤12%; crude fat ≥5%; crude ash ≤15%; total phosphorus ≥1%; moisture ≤12.5%; lysine ≥1.6%) was used, with a daily feeding rate of 4% of the tilapia's body weight. Based on the calculation that 62% of the total nitrogen (TN) from supplemental feed is released into the environment, 1.488 g of feed was added to the reactor daily to simulate the actual aquaculture environment.

[0102] Carbon-to-nitrogen ratio control: The nitrogen content of the feed was calculated based on the crude protein content (31%) and the average nitrogen content in the protein (16%); the carbon content of the carbon source was calculated based on the carbon content of glucose (40%). To maintain a carbon-to-nitrogen ratio of 15 in the water, it was calculated that 1.86g of glucose needs to be added per 1g of feed. In this embodiment, 1.488g of feed was fed into the reactor daily through a carbon source supplementation device, therefore 2.768g of glucose needed to be added daily to ensure the normal metabolism of microorganisms in the bioflocs.

[0103] Aeration and Electrical Performance Monitoring: Turn on oxygen pump 8, causing aeration head 7 to aerate upwards. Adjust the aeration rate to create a relatively anaerobic environment for the anode and an oxygen-rich environment for the cathode; specifically, set the aeration rate to 25-50 L / min. Since anode 6 is placed below aeration head 7 and aeration head 7 aerates upwards, a relatively anaerobic environment (DO < 2 mg / L) is created for anode 6, and an oxygen-rich environment (DO > 5 mg / L) is created for cathode 5, ensuring the smooth progress of the redox reaction of microorganisms in the MFC component, while providing suitable dissolved oxygen conditions for microorganisms in biofloc 4.

[0104] Adjust the external circuit resistance of the MFC component to 1000Ω, turn on the electrical performance monitoring device, and record the output voltage and current in real time. At regular intervals, when it is necessary to measure the polarization curve and power density curve, adjust the resistance box to 10Ω~9999Ω, collect the voltage and current values ​​under different resistances, plot the polarization curve and calculate the maximum surface power density.

[0105] Water quality monitoring: Dissolved oxygen (DO), pH, and temperature of the aquaculture water are measured daily using a water quality monitoring device, with each measurement interval not exceeding 30 minutes. Ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen content are measured every two days. Before measurement, flocculation sedimentation is used to remove floc color interference: 100 mL of water sample is taken, 1 mL of 10% (w / v) ZnSO4 solution is added, and 25% (w / v) NaOH solution is added to adjust the pH to approximately 10.5. The mixture is then stirred. After standing for 5-15 minutes until sufficient sedimentation, the sample is filtered through medium-speed filter paper thoroughly washed with ammonia-free water. 20 mL of the initial filtrate is discarded, and the remaining filtrate is used for ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen detection. Total suspended solids (TSS) and floc volume are measured every 15 days using a biofloc characterization device to monitor the system's operational status.

[0106] Water management: The entire system achieves zero discharge of aquaculture wastewater, without actively discharging aquaculture tailwater. Throughout the operation, the aquaculture water body is not replaced; only water lost due to sampling and natural evaporation is replenished, achieving zero-discharge operation and significantly conserving water resources.

[0107] Example 3: Testing the operational effectiveness of the novel aquaculture system of the present invention.

[0108] For the coupled system in Example 2 (experimental group, such as...) Figure 2 (as shown) and a single BFT system (control group, such as) Figure 1 The operational performance (as shown) was continuously monitored over a period of 48 days, with TN and TOC being monitored for an additional 20 days after the 48th day. The main monitoring results are as follows:

[0109] Basic water quality indicators (such as) Figures 3 to 7As shown in the figure): the DO, pH and temperature of the experimental group and the control group remained stable, the DO was maintained at a high level, the pH was maintained between 7.7 and 8.7, and the temperature was controlled at 25℃ after the 11th day of the experiment, all of which were suitable for the growth of microorganisms and tilapia; the DO of the experimental group showed a continuous upward trend in the daily cycle, because oxygen was produced in the power generation process of MFC.

[0110] Nitrogen index (such as) Figures 8 to 11 As shown in the figure): the ammonia nitrogen concentration in the experimental group remained stable below 0.20 mg / L throughout the process, with no obvious peak, while the ammonia nitrogen concentration in the control group fluctuated and increased from day 12, reaching a peak of 0.56 mg / L; the nitrite nitrogen concentration in the experimental group fluctuated slightly within a safe range, and the nitrate nitrogen decreased to 0 mg / L simultaneously with the control group, achieving efficient denitrification; the peak TN content in the experimental group was 12.87 mg / L, which was significantly lower than the 23.55 mg / L in the control group.

[0111] TOC indicators (such as) Figure 12 As shown in the figure): the TOC content in the experimental group was lower than that in the control group, and the peak value was significantly lower than that in the control group. The TOC removal capacity of the coupled system was better than that of the single BFT system.

[0112] Biofloc indicators (such as) Figure 13 As shown in the figure): the growth rate of floc volume in the experimental group was significantly lower than that in the control group, and the floc volume was lower than that in the control group throughout the entire process. This effectively reduced the turbidity of the aquaculture water, prevented tilapia gill blockage, and did not affect the water purification effect.

[0113] Electrical performance indicators (such as) Figures 14 to 18 As shown in the figure): The output voltage of the experimental group MFC module (anode 6 and cathode 5) showed a fluctuating upward trend, reaching a maximum of 295.9mV; the surface power density initially rose rapidly to about 1600mW / m², and maintained a high level in the middle period, with a maximum surface power density of 1716.8mW / m²; within the daily cycle, the voltage and power density dropped briefly after feeding, but then recovered quickly, and the system had good self-recovery ability.

[0114] The above test results show that the BFT-MFC coupled aquaculture system of the present invention is significantly better than the single BFT system in terms of water purification, floc control and energy recovery. Moreover, the system is stable in operation and has strong anti-interference ability, realizing high-density zero-emission aquaculture of tilapia.

[0115] This invention constructs an energy-self-sufficient, low-carbon-emission BFT-MFC coupled system, which exhibits significant advantages in both water purification capacity and operational stability. Experimental results show that its removal efficiency for ammonia nitrogen, total nitrogen, and total organic carbon is superior to that of a single BFT system. Simultaneously, the system effectively reduces water turbidity, minimizing the risk of gill blockage in fish without adversely affecting water purification, indicating better adaptability to actual aquaculture environments. Furthermore, the coupled system demonstrates continuous and stable power output during operation, with a maximum output voltage of 295.9 mV and a maximum areal power density of 1716.8 mW / m², possessing good energy recovery potential and providing a possibility for energy self-sufficiency in aquaculture systems. Data from continuous operation for over 48 days also confirms that the system has strong anti-interference capabilities and operational stability, maintaining good water purification effects and power output performance. Analysis shows that the BFT and MFC in the coupled system are functionally complementary. The unused carbon source and incompletely decomposed organic matter of the BFT can serve as substrates for the MFC, avoiding carbon source waste. The MFC electrode provides an attachment interface for microorganisms, promoting the optimization of floc structure. This invention achieves in-situ zero-discharge purification of aquaculture water. A single carbon source addition simultaneously supplies BFT biological metabolism, "activates" the MFC for electricity generation, and then uses microcurrent excitation to enhance denitrification. The system has a simple structure, low operating cost, and high stability, making it suitable for small and medium-sized aquaculture farms.

[0116] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0117] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coupling system for aquaculture bioflocs and microbial fuel cells, characterized in that, The reactor includes a main body for aquaculture, which is filled with aquaculture water containing bioflocs (4), and also includes a microbial fuel cell assembly and an aeration device. The microbial fuel cell assembly includes an anode (6), a cathode (5), and an external circuit. The anode (6) is located at the bottom of the reactor body, the cathode (5) is located at the top of the reactor body, and the external circuit connects the anode (6) and the cathode (5). The aeration device includes an aeration head (7) and an oxygen pump (8). The oxygen pump (8) is connected to the aeration head (7) through an air pipe and is used to provide compressed air to the aeration head (7). The aeration head (7) is suspended directly above the anode (6) and the air outlet direction is upward. The upward aeration creates a relatively anaerobic environment for the anode (6) and an oxygen-rich environment for the cathode (5).

2. The aquaculture biofloc and microbial fuel cell coupling system according to claim 1, characterized in that, The main body of the aquaculture reactor is an acrylic cylindrical structure.

3. The aquaculture biofloc and microbial fuel cell coupling system according to claim 1, characterized in that, The external circuit includes an adjustable resistance box (1), an ammeter (2) and a digital multimeter; the adjustable resistance box (1) and the ammeter (2) are connected in series and then connected to the circuit between the anode (6) and the cathode (5); the digital multimeter is connected in parallel across the two ends of the adjustable resistance box (1); the anode (6) and the cathode (5) are connected by a copper-plated nickel wire (3) through the external circuit. Both the anode (6) and the cathode (5) use carbon felt as electrode material. The electrode dimensions are: length 10~20 cm, width 10~20 cm, thickness 0.5~2 cm, and the distance between the anode and cathode is 20~40 cm. Furthermore, no proton exchange membrane is provided in the microbial fuel cell assembly.

4. The aquaculture biofloc and microbial fuel cell coupling system according to claim 1, characterized in that, The aeration device is an adjustable aeration head.

5. The aquaculture biofloc and microbial fuel cell coupling system according to claim 1, characterized in that, The reactor body is externally connected to a power generation performance monitoring device, which is connected to the external circuit of the microbial fuel cell assembly and is used to collect and record the output voltage and current in real time. The formula for calculating the surface current density detected by the power generation performance monitoring device is as follows: ， The formula for calculating surface power density is: ， Where U is the output voltage, R is the external circuit resistance, and A is the anode surface area.

6. A method for operating a coupling system of aquaculture bioflocs and microbial fuel cells according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Add aquaculture water containing bioflocs (4) into the main body of the aquaculture reactor, control the aquaculture density, feed the aquaculture feed according to the weight ratio of the aquaculture animals, and at the same time maintain the carbon-nitrogen ratio of the water by supplementing carbon sources. Step S2: Turn on the aeration head (7) to aerate upwards at the preset aeration rate, so that the anode (6) area is in a relatively anaerobic environment and the cathode (5) area is in an oxygen-rich environment. Step S3: Adjust the adjustable resistance box (1) of the external circuit to the preset resistance value and record the output voltage and current in real time; when measuring the polarization curve and power density curve, adjust the resistance box to different resistance values ​​and collect the corresponding voltage and current values. Step S4: Regularly monitor dissolved oxygen, pH, temperature, and the content of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total nitrogen, total organic carbon, total suspended solids, and floc volume in the aquaculture water.

7. The operation method of the aquaculture biofloc and microbial fuel cell coupling system according to claim 6, characterized in that, The aquaculture density is 1.5-2.5 kg / m³, and the feed is given at 2-5% of the body weight of the farmed animals. The carbon-nitrogen ratio in the water is 10-20. The aeration rate is 25-50 L / min, so that the dissolved oxygen concentration in the anode (6) region is <2 mg / L and the dissolved oxygen concentration in the cathode (5) region is >5 mg / L; The adjustable resistance box of the external circuit is adjusted to 500-1000 Ω during normal operation and to 10-9999 Ω when measuring polarization curves and power density curves. Dissolved oxygen, pH, and temperature are measured daily; ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total nitrogen, and total organic carbon content are measured every 1-3 days; and total suspended solids and floc volume are measured every 10-15 days. The carbon source is an organic carbon source; The aquaculture feed is an extruded compound feed for aquaculture with a crude protein content of ≥31%.

8. The operation method of the aquaculture biofloc and microbial fuel cell coupling system according to claim 6, characterized in that, The cultivation method of the biofloc (4) is as follows: Brown sugar and a compound bacterial agent including Bacillus subtilis were inoculated into the water. The temperature was controlled at >10℃, dissolved oxygen at >5 mg / L, and the carbon-nitrogen ratio was maintained at 10-20. After 15 days of cultivation, bioflocs with an initial total suspended solids concentration of 7-9 mg / L were obtained (4).

9. The operation method of the aquaculture biofloc and microbial fuel cell coupling system according to claim 6, characterized in that, The carbon felt electrodes of the anode (6) and cathode (5) are pretreated before use: Soak the carbon felt in anhydrous ethanol for 30 minutes, then rinse with deionized water. Then, it was treated in 0.1 mol / L hydrochloric acid solution at 80-100℃ for 30 min, rinsed with deionized water until neutral, and dried at 80℃ for 24 h; finally, it was soaked in biofloc (4) for 48 h for microbial enrichment.

10. The operation method of the aquaculture biofloc and microbial fuel cell coupling system according to claim 6, characterized in that, Before detecting the content of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen, flocculation and precipitation methods are used to remove the color interference of flocs.

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