Ammonia-nitrogen low-carbon treatment system and method for high-density culture circulating water system

Abstract

The invention belongs to the technical field of aquaculture wastewater treatment, and particularly discloses an ammonia nitrogen low-carbon treatment system and method for a high-density aquaculture circulating water system.The system comprises an SND biological denitrification unit and an ultraviolet electro-catalysis advanced treatment unit which are sequentially communicated, the monitoring regulation and control module is electrically connected with the SND biological denitrification unit and the ultraviolet electro-catalysis advanced treatment unit; the SND biological denitrification unit comprises a reaction tank, a carbon source adding assembly, an aeration system and a modified polyurethane biological carrier filled in the reaction tank. According to the ammonia nitrogen low-carbon treatment system and method for the high-density culture circulating water system, efficient removal of ammonia nitrogen in culture water is achieved, meanwhile, carbon source consumption and energy consumption are greatly reduced, the operation stability of the system is guaranteed, no toxic by-product is generated, the treated water body can directly flow back for culture, and the requirement for the growth water quality of mandarin fish is met.

Description

Technical Field

[0001] This invention relates to the field of aquaculture wastewater treatment technology, and in particular to a low-carbon ammonia nitrogen treatment system and method for a high-density aquaculture recirculating water system. Background Technology

[0002] Factory-scale high-density mandarin fish farming is an important model of modern aquaculture, with advantages such as high stocking density, large yield, and no restrictions from the natural environment. However, due to the large amount of feed and vigorous metabolism of mandarin fish during the farming process, the ammonia nitrogen concentration in the farming water can easily reach 3-5 mg / L. The tolerance threshold of mandarin fish to ammonia nitrogen is only ≤0.5 mg / L. Excessively high ammonia nitrogen concentration will lead to slow growth, reduced survival rate, and even large-scale mortality of mandarin fish, which has become the core problem restricting the development of factory-scale high-density mandarin fish farming.

[0003] Currently, traditional ammonia nitrogen treatment technologies for aquaculture water have many significant drawbacks: traditional biological denitrification technologies require the addition of large amounts of carbon sources, with a carbon-to-nitrogen ratio of ≥15:1, which not only results in high treatment costs but also easily leads to eutrophication of the water body due to excessive carbon sources, causing further deterioration of water quality; single physicochemical treatment methods, such as breakpoint chlorination, can quickly remove ammonia nitrogen, but they easily produce toxic byproducts such as chloramines and trihalomethanes, which seriously threaten the survival safety of mandarin fish; some existing integrated treatment technologies do not fully consider the physiological characteristics of mandarin fish, which prefer slightly alkaline and low-disturbance water, resulting in poor stability of the denitrification process, and even slight fluctuations in the influent ammonia nitrogen concentration can lead to a significant decrease in treatment efficiency.

[0004] Simultaneous nitrification-denitrification (SND) technology can directly convert ammonia nitrogen to N2 in the same reactor, saving more than 30% of carbon source compared to traditional biological denitrification. However, under the condition of low C / N ratio in aquaculture wastewater, the activity of denitrifying bacteria is low, making it difficult to achieve stable operation. Ultraviolet photoelectrocatalytic oxidation technology can efficiently degrade residual ammonia nitrogen and recalcitrant organic matter in water bodies, but when used alone, the energy consumption is extremely high. When applied to large-scale aquaculture water recycling treatment, the operating cost is too high, making it impossible to promote industrialization.

[0005] Therefore, developing an ammonia nitrogen treatment technology that is suitable for the weakly alkaline and low-disturbance water quality characteristics of mandarin fish farming, and that combines high denitrification efficiency, low carbon source consumption, low energy consumption, stable operation, and no toxic byproducts, is the key to solving the ammonia nitrogen pollution problem in factory-scale high-density mandarin fish farming, and is also a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a low-carbon ammonia nitrogen treatment system and method for high-density aquaculture recirculating water systems, which achieves efficient removal of ammonia nitrogen from aquaculture water, while significantly reducing carbon source consumption and energy consumption, ensuring system operational stability, and generating no toxic byproducts. The treated water can be directly recycled back to aquaculture, which is suitable for the water quality requirements for mandarin fish growth.

[0007] To achieve the above objectives, the present invention provides an ammonia nitrogen and low carbon treatment system for a high-density aquaculture recirculating water system, comprising an SND biological denitrification unit and an ultraviolet photoelectrocatalytic deep treatment unit connected in sequence, and further comprising a monitoring and control module electrically connected to both the SND biological denitrification unit and the ultraviolet photoelectrocatalytic deep treatment unit. The SND biological denitrification unit includes a reaction tank, a carbon source addition component, an aeration system, and a modified polyurethane biological carrier filled in the reaction tank. The inlet of the reaction tank is used to connect to the drainage outlet of the aquaculture pond. The aeration system adopts a microporous aeration method. The carbon source addition component is a peristaltic pump type addition structure with high addition accuracy, which can realize the quantitative and continuous addition of carbon source. The ultraviolet photoelectrocatalytic deep treatment unit includes a buffer tank, a photoelectrocatalytic reactor, and a reflux pump connected in sequence. The buffer tank is used to temporarily store the water after treatment by the SND biological denitrification unit to avoid the effect of water flow fluctuation on the photoelectrocatalytic treatment effect. The photoelectrocatalytic reactor has built-in electrodes with Sn-doped TiO2 / CNTs composite catalyst coating, ultraviolet lamps, and DC power supply. The DC power supply is used to apply an external bias voltage of 0.8~1.2V to the electrodes. The monitoring and control module includes a pH sensor, an online ammonia nitrogen monitor, and a PLC controller. The detection ends of the pH sensor and the online ammonia nitrogen monitor extend into the reaction tank and the photoelectrocatalytic reactor, respectively. The PLC controller is electrically connected to the carbon source dosing component, the aeration system, and the DC power supply. It can dynamically adjust the operating parameters of each unit according to the real-time detection data to realize the intelligent and automated operation of the system.

[0008] Preferably, the microporous aeration method specifically involves: evenly arranging aeration discs at the bottom of the reaction tank and setting a dissolved oxygen gradient along the water flow direction (3~4 mg / L at the inlet and 5~6 mg / L at the outlet) to meet the micro-oxygen environment requirements of SND simultaneous nitrification and denitrification.

[0009] Preferably, the modified polyurethane biocarrier has a specific surface area ≥ 800 m². 2 / g, which is conducive to the attachment and reproduction of denitrifying functional bacteria. The modified polyurethane biocarrier has a porous mesh structure with a porosity of 80%~90%, and the modified polyurethane biocarrier is attached with denitrifying functional bacteria.

[0010] The modified polyurethane biocarrier was prepared by etching commercial PU foam with NaOH solution (5~10wt%, 60℃, 2~4h) to improve surface energy and hydrophilicity, drying, immersing in FeSO4 / FeCl3 solution (0.1~0.5mol / L) and vacuum impregnating for 30~60min to allow iron salts to penetrate into the foam pores, washing with water and vacuum drying to obtain the hydrophilic-nFe-PU carrier.

[0011] The denitrification functional bacterial community is a complex of nitrifying and denitrifying bacteria. The nitrifying bacteria consist of *Nitrosomonas* and *Nitrobacterium*, with a ratio of 3:2. The denitrifying bacteria consist of *Pseudomonas* and *Rhodomorphobacter*, with a ratio of 4:1. This complex bacterial community is subjected to low C / N ratio (8:1), weak alkalinity (pH 7.5~8.5), and low disturbance (hydraulic shear force ≤0.05 N / m). 2 The compound selection and acclimatization method, with an inoculation amount of 5-8% (by volume), is suitable for the weakly alkaline and low-disturbance water environment of mandarin fish farming.

[0012] Preferably, the Sn doping amount in the Sn-doped TiO2 / CNTs composite catalyst coating is 5%, and the electrode is prepared by the sol-gel method and loaded onto the surface of the titanium sheet electrode to form the electrode.

[0013] Preferably, the sol-gel method specifically involves: dissolving tetrabutyl titanate in anhydrous ethanol to form a homogeneous alcoholic solution; adding tin chloride at a Sn / Ti molar ratio of 5%, stirring until completely dissolved, adding carbon nanotubes with a diameter of 10-20 nm, and ultrasonically dispersing for 30-60 min to obtain a stable suspension; slowly adding a dilute ethanol solution to form a homogeneous transparent sol, allowing it to age at room temperature, vacuum drying at 80°C for 12 h, and then calcining it in a muffle furnace at 500°C for 2 h to obtain a Sn-doped TiO2 / CNTs composite catalyst.

[0014] Sn-doped TiO2 / CNTs composite catalyst is mixed with ethanol solution and ultrasonically dispersed to form a uniform coating slurry. The slurry is then uniformly coated onto the surface of a titanium sheet, dried in an oven at low temperature, and finally heat-treated at 100~150℃ for 30 minutes to cure, thus obtaining the electrode.

[0015] Preferably, the reaction tank is connected to a pH adjustment component, which includes a sodium bicarbonate storage tank, a metering pump, and a dosing pipeline. The metering pump is electrically connected to the PLC controller, and the outlet end of the dosing pipeline extends into the reaction tank.

[0016] Preferably, the ultraviolet lamp has a wavelength of 254nm and a power of 50W. The ultraviolet lamp and the electrode are arranged alternately in the photoelectrocatalytic reactor, with the ultraviolet lamp 5-8cm away from the electrode to ensure uniform light intensity in the reactor.

[0017] Preferably, a liquid level sensor is installed in the buffer tank, and the liquid level sensor is electrically connected to the PLC controller to realize automatic control of the flow rate of water introduced into the photoelectrocatalytic reactor.

[0018] Preferably, the carbon source dosing component uses a special composite carbon source made of glucose and polyhydroxyalkanoates, with a glucose to polyhydroxyalkanoates mass ratio of 3-5:1. This combination provides both fast-acting and long-lasting carbon sources, ensuring continuous energy supply to the denitrifying bacteria. The carbon source is added in stages: 70% is added at the inlet and 30% in the middle of the reaction tank, avoiding localized overdose.

[0019] This invention also provides a method for low-carbon ammonia nitrogen treatment in a high-density aquaculture recirculating aquaculture system, comprising the following steps: S1. Aquaculture water circulation introduction: The high ammonia nitrogen aquaculture water in the aquaculture pond is introduced into the reaction tank at a circulation rate of 50~80% / h. The ammonia nitrogen concentration of the influent is detected in real time by an online ammonia nitrogen monitor. The PLC controller automatically calculates the carbon source addition amount according to the detection data and the formula: addition amount = ammonia nitrogen concentration × carbon-nitrogen ratio × water flow rate. S2 and SND simultaneous nitrification and denitrification treatment: The carbon source addition component adds a special composite carbon source of glucose and polyhydroxyalkanoate into the reaction tank according to the instructions of the PLC controller, controlling the carbon-nitrogen ratio in the reaction tank to be 8~12:1. At the same time, the aeration system maintains the dissolved oxygen concentration in the reaction tank at 2~4mg / L to meet the dissolved oxygen requirements of simultaneous nitrification and denitrification. The denitrification functional bacteria attached to the modified polyurethane biological carrier realize the simultaneous nitrification and denitrification of ammonia nitrogen, initially removing ammonia nitrogen from the water body with an initial removal rate of more than 85%. S3, Real-time pH Control: During the SND simultaneous nitrification and denitrification process, the pH sensor monitors the acidity and alkalinity of the water in the reaction tank in real time. When pH < 7.5, the PLC controller controls the pH adjustment component to add sodium bicarbonate to the tank to adjust the pH of the water to a suitable range for the activity of denitrifying bacteria (pH 7.5~8.5) and ensure the stable metabolism of the denitrifying bacteria. S4. Photoelectrocatalytic deep treatment: The water treated by the SND biological denitrification unit is temporarily stored in a buffer tank, and then introduced into the photoelectrocatalytic reactor at a uniform speed. An external bias voltage of 0.8~1.2V is applied to the Sn-doped TiO2 / CNTs composite catalyst coating electrode, and a 254nm ultraviolet lamp is turned on. Through the synergistic effect of the Sn-doped TiO2 / CNTs composite catalyst and ultraviolet light, the residual ammonia nitrogen and recalcitrant organic matter in the water are deeply oxidized, reducing the residual ammonia nitrogen to below 0.1mg / L. S5. Purified water return: The water that has undergone photoelectrocatalytic deep treatment is directly returned to the aquaculture pond through a return pump, completing the circulation and purification of the aquaculture water.

[0020] Preferably, in S1, the concentration of ammonia nitrogen in the influent fluctuates within the range of 1~5 mg / L.

[0021] Preferably, in S2, the hydraulic retention time in the reaction tank is 4~6 hours; In S4, the hydraulic residence time in the photoelectrocatalytic reactor is 1~2h.

[0022] Preferably, in S2, the hydraulic retention time in the reaction tank is 5 hours; In S4, the hydraulic residence time in the photoelectrocatalytic reactor is 1.5 h.

[0023] Preferably, when the method is applied to factory-scale high-density mandarin fish farming, the stocking density in the culture pond is 50 fish / m². 3 During continuous operation, the ammonia nitrogen level in the mandarin fish farming water remained stable at 0.05~0.12 mg / L.

[0024] Therefore, the ammonia nitrogen and low carbon treatment system and method for a high-density aquaculture recirculating aquaculture system described above have the following beneficial effects: High denitrification efficiency and excellent effluent quality: This invention adopts an integrated process of SND biological denitrification and ultraviolet photoelectrocatalytic deep treatment. The front section removes the main ammonia nitrogen, and the back section deeply oxidizes the residual ammonia nitrogen. The total ammonia nitrogen removal rate of the system reaches more than 98.5%, and the ammonia nitrogen concentration in the effluent is reduced to 0.1 mg / L, which is far below the tolerance threshold of mandarin fish and meets the GB 11607-1989 "Fishery Water Quality Standard". The treated water can be directly recycled for aquaculture.

[0025] Easy to operate and low operating cost: This invention reduces the carbon-to-nitrogen ratio to 8-12:1 by combining a special composite carbon source of glucose and polyhydroxy fatty acid ester with denitrifying bacteria. The carbon source consumption is reduced by 42% compared with traditional biological denitrification technology, which greatly reduces the operating cost of the system. By linking various detection sensors and execution components through a PLC controller, the intensity of manual operation is reduced, making it suitable for industrial application in large-scale factory farming.

[0026] Stable operation and strong shock resistance: Through intelligent and automated control of the monitoring and regulation module, combined with denitrifying bacteria and process parameters adapted to the mandarin fish farming environment, the total ammonia nitrogen removal rate of the system fluctuates within the range of 1~5 mg / L when the influent ammonia nitrogen fluctuates, the stability is improved, and it can adapt to the dynamic changes in ammonia nitrogen concentration in factory farming.

[0027] No toxic byproducts, suitable for mandarin fish growth: This invention does not add chlorine or other agents that easily produce toxic byproducts throughout the process. The SND biological denitrification process is mild, and the photoelectrocatalytic deep treatment achieves ammonia nitrogen degradation only through catalytic oxidation. Moreover, the entire process takes into account the water quality characteristics of mandarin fish, which prefer slightly alkaline and low-disturbance water. The water quality indicators of the treated water are highly matched with the growth requirements of mandarin fish.

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0029] Figure 1This is a schematic diagram of an embodiment of an ammonia nitrogen and low carbon treatment system and method for a high-density aquaculture recirculating water system according to the present invention; Figure 2 This is a monitoring change diagram of an embodiment of the ammonia nitrogen low-carbon treatment system and method for a high-density aquaculture recirculating water system of the present invention.

[0030] Figure Labels 1. pH sensor; 2. Ammonia nitrogen online monitor; 3. PLC controller; 4. Reaction tank; 5. Carbon source dosing assembly; 6. Aeration system; 7. Buffer tank; 8. Photoelectrocatalytic reactor; 9. Reflux pump; 10. Electrode; 11. Ultraviolet lamp; 12. DC power supply; 13. Liquid level sensor; 14. Sodium bicarbonate storage tank; 15. Metering pump; 16. Dosing pipeline. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0033] like Figure 1 As shown, the system in all embodiments of the present invention includes an SND biological denitrification unit and an ultraviolet photoelectrocatalytic deep treatment unit connected in sequence, and also includes a monitoring and control module electrically connected to both the SND biological denitrification unit and the ultraviolet photoelectrocatalytic deep treatment unit. The monitoring and control module includes a pH sensor 1, an online ammonia nitrogen monitor 2, and a PLC controller 3. The SND biological denitrification unit includes a reaction tank 4, a carbon source addition component 5, an aeration system 6, and a modified polyurethane biological carrier filled in the reaction tank 4. The aeration system 6 uses aeration discs, which are evenly arranged at the bottom of the reaction tank 4. The carbon source addition component 5 is respectively set at the inlet end and the middle section of the reaction tank 4.

[0034] The ultraviolet photoelectrocatalytic deep treatment unit includes a buffer tank 7, a photoelectrocatalytic reactor 8, and a reflux pump 9 connected in sequence. The photoelectrocatalytic reactor 8 houses an electrode 10 with a Sn-doped TiO2 / CNTs composite catalyst coating, an ultraviolet lamp 11, and a DC power supply 12. The ultraviolet lamp 11 and the electrode 10 are arranged alternately within the photoelectrocatalytic reactor 8. A level sensor 13 is installed in the buffer tank 7 and is electrically connected to a PLC controller 3. The detection ends of the pH sensor 1 and the ammonia nitrogen online monitor 2 extend into the reaction tank 4 and the photoelectrocatalytic reactor 8, respectively. The PLC controller 3 is also electrically connected to the carbon source dosing component 5, the aeration system 6, and the DC power supply 12.

[0035] In addition, the reaction tank 4 is connected to a pH adjustment component, which includes a sodium bicarbonate storage tank 14, a metering pump 15 and a dosing pipeline 16. The metering pump 15 is electrically connected to the PLC controller 3, and the discharge end of the dosing pipeline 16 extends into the reaction tank 4.

[0036] Example 1 A low-carbon ammonia nitrogen treatment system for a high-density aquaculture recirculating aquaculture system, specifically a laboratory-scale test, includes an SND biological denitrification unit, an ultraviolet photoelectrocatalytic deep treatment unit, and a monitoring and control module. The SND biological denitrification unit includes a reaction tank 4 filled with a modified polyurethane biological carrier. In this embodiment, a 5L reaction tank 4 is used, filled with 2L of modified polyurethane biological carrier, which has a specific surface area of ​​850m². 2 / g. The ultraviolet photoelectrocatalytic deep treatment unit includes a buffer water tank 7, a photoelectrocatalytic reactor 8, and the photoelectrocatalytic reactor 8 has a built-in electrode 10, an ultraviolet lamp 11, and a DC power supply 12. In this embodiment, the buffer water tank 7 has a volume of 1L; the photoelectrocatalytic reactor 8 has a volume of 2L; and the electrode 10 has an area of ​​0.1m². 2 Sn doping content 5%; UV lamp 11 wavelength 254nm, power 50W, electrode 10 and UV lamp 11 spacing 5cm; DC power supply 12 adjustable bias voltage 0~2V; monitoring and control module includes pH sensor 1, ammonia nitrogen online monitor 2 and small PLC controller 3.

[0037] The specific operation process is as follows: Wastewater from factory-farmed mandarin fish farming was used as the treatment sample, with an initial ammonia nitrogen concentration of 4.2 mg / L. The sample was introduced into reaction tank 4 at a circulation rate of 60% / h, with the carbon-to-nitrogen ratio controlled at 10:1. A special composite carbon source (mass ratio 4:1) of glucose and polyhydroxyalkanoate was added. The hydraulic retention time of the SND unit was 5 h, and the aeration system 6 maintained a dissolved oxygen concentration of 3 mg / L. The photoelectrocatalytic unit was subjected to an external bias voltage of 1.0 V, with a hydraulic retention time of 1.5 h. The pH sensor 1 monitored the water in real time to maintain the pH of the water body at ≥7.5.

[0038] Treatment results: The SND biological denitrification unit achieved an ammonia nitrogen removal rate of 87%, with an effluent ammonia nitrogen concentration of 0.546 mg / L. After ultraviolet photoelectrocatalytic advanced treatment, the residual ammonia nitrogen in the water decreased to 0.06 mg / L, the total ammonia nitrogen removal rate of the system was 98.6%, the carbon source consumption was 0.8 g / L, and the energy consumption of the photoelectrocatalytic unit was 0.3 kWh / m³. 3 Water, without the formation of toxic byproducts.

[0039] Example 2 The difference from Example 1 is that the initial concentration of ammonia nitrogen was set to 1 mg / L.

[0040] Treatment results: The SND biological denitrification unit achieved a removal rate of 87% for ammonia nitrogen, with an effluent ammonia nitrogen concentration of 0.546 mg / L. After ultraviolet photoelectrocatalytic deep treatment, the residual ammonia nitrogen in the water was reduced to 0.06 mg / L, and the total ammonia nitrogen removal rate of the system was 98.9%, with a removal rate fluctuation of ≤0.3%.

[0041] Example 3 The difference from Example 1 is that the initial concentration of ammonia nitrogen was set to 3 mg / L.

[0042] Treatment results: The SND biological denitrification unit achieved a removal rate of 87% for ammonia nitrogen, with an effluent ammonia nitrogen concentration of 0.546 mg / L. After ultraviolet photoelectrocatalytic deep treatment, the residual ammonia nitrogen in the water was reduced to 0.06 mg / L, and the total ammonia nitrogen removal rate of the system was 98.7%, with a removal rate fluctuation of ≤0.3%.

[0043] Example 4 A low-carbon ammonia nitrogen treatment system for a high-density aquaculture recirculating aquaculture system, specifically a pilot-scale industrial system, includes a sequentially connected SND biological denitrification unit and an ultraviolet photoelectrocatalytic deep treatment unit. It also includes a monitoring and control module electrically connected to both the SND biological denitrification unit and the ultraviolet photoelectrocatalytic deep treatment unit. The monitoring and control module includes a pH sensor 1, an online ammonia nitrogen monitor 2, and a PLC controller 3. The PLC controller 3 is an industrial-grade PLC control system that links all detection and execution components.

[0044] The SND biological denitrification unit includes a reaction tank 4, a carbon source addition component 5, an aeration system 6, and a modified polyurethane biological carrier filled within the reaction tank 4. The reaction tank 4 is connected to a 100m³... 3 Factory-style mandarin fish farming ponds with a stocking density of 50 fish / m³ 3 Circulating water volume 60m³ 3 / h (circulation rate 60% / h). The effective volume of reaction tank 4 is designed according to the circulating water volume. Carbon source addition component 5 is an industrial-grade peristaltic pump, and aeration system 6 adopts microporous aeration.

[0045] The ultraviolet photoelectrocatalytic deep treatment unit comprises a buffer water tank 7, a photoelectrocatalytic reactor 8, and a reflux pump 9 connected in sequence. The buffer water tank 7 has a volume of 5 m³. 3 The photoelectrocatalytic reactor 8 has multiple sets of electrodes 10 and ultraviolet lamps 11 arranged alternately with a spacing of 8cm, and the applied bias voltage is dynamically adjusted from 0.9 to 1.1V.

[0046] The specific operation process is as follows: The carbon-to-nitrogen ratio of the SND unit is controlled at 9:1, and a special composite carbon source of glucose and polyhydroxyalkanoate (mass ratio 3.5:1) is added. The dissolved oxygen concentration is 2.5~3.5 mg / L, and the hydraulic retention time is 5h. The hydraulic retention time of the photoelectrocatalytic unit is controlled at 1.5h, and the bias voltage is dynamically adjusted according to the ammonia nitrogen concentration of the influent. The pH of the water body is maintained at 7.5~8.5 throughout the process.

[0047] Running result: The system operated continuously and stably for 30 days, maintaining ammonia nitrogen levels in the mandarin fish farming water consistently between 0.05 and 0.12 mg / L, far below the tolerance threshold for mandarin fish. The energy consumption of the photoelectrocatalytic unit remained stable at 0.3 kWh / m³. 3 water.

[0048] Comparative Example 1 A high-density aquaculture recirculating aquaculture system employing biological denitrification technology, connected to a 100m... 3 Factory-style mandarin fish farming ponds with a stocking density of 50 fish / m³ 3 The difference from Example 4 is that only a single SND biological denitrification unit is set up, and the system runs continuously for 30 days.

[0049] Test Carbon source consumption, mandarin fish survival rate, and feed conversion ratio were monitored during the aquaculture process of Example 4 and Comparative Example 1. The results of carbon source consumption are as follows: Figure 2 As shown.

[0050] Depend on Figure 2 It can be seen that during the aquaculture process, the carbon source consumption fluctuates to some extent due to factors such as water temperature, dissolved oxygen, uneaten feed, feces, and microbial activity. Overall, the carbon source consumption in Comparative Example 1 is 12.5 kg / 30 days, while that in Example 4 is 7.25 kg / 30 days, representing a 42% reduction. Furthermore, the survival rate of mandarin fish in Comparative Example 1 is 82%, while that in Example 4 is 92%, representing a 12% increase. The feed conversion ratio (FCR) in Comparative Example 1 is 1.85, while that in Example 4 is 1.70, a 0.15 reduction. This significantly improves the aquaculture efficiency. The treated water is directly recycled back to the aquaculture, resulting in no secondary pollution.

[0051] Therefore, the present invention adopts the above-mentioned ammonia nitrogen low-carbon treatment system and method for a high-density aquaculture recirculating water system to achieve efficient removal of ammonia nitrogen from aquaculture water, while significantly reducing carbon source consumption and energy consumption, ensuring system operation stability, and generating no toxic byproducts. The treated water can be directly returned to aquaculture, which is suitable for the growth water quality requirements of mandarin fish.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A low-carbon ammonia nitrogen treatment system for a high-density aquaculture recirculating aquaculture system, characterized in that: It includes an SND biological denitrification unit and an ultraviolet photoelectrocatalytic deep treatment unit connected in sequence, and also includes a monitoring and control module electrically connected to both the SND biological denitrification unit and the ultraviolet photoelectrocatalytic deep treatment unit. The SND biological denitrification unit includes a reaction tank, a carbon source addition component, an aeration system, and a modified polyurethane biological carrier filled in the reaction tank. The inlet of the reaction tank is used to connect to the outlet of the aquaculture pond. The aeration system adopts a microporous aeration method. The carbon source addition component is a peristaltic pump type addition structure. The ultraviolet photoelectrocatalytic deep processing unit includes a buffer water tank, a photoelectrocatalytic reactor, and a reflux pump connected in sequence. The photoelectrocatalytic reactor has built-in electrodes with Sn-doped TiO2 / CNTs composite catalyst coating, an ultraviolet lamp, and a DC power supply. The DC power supply is used to apply an external bias voltage of 0.8~1.2V to the electrodes. The monitoring and control module includes a pH sensor, an online ammonia nitrogen monitor, and a PLC controller. The detection ends of the pH sensor and the online ammonia nitrogen monitor extend into the reaction tank and the photoelectrocatalytic reactor, respectively. The PLC controller is electrically connected to the carbon source dosing component, the aeration system, and the DC power supply.

2. The ammonia nitrogen and low-carbon treatment system for a high-density aquaculture recirculating aquaculture system according to claim 1, characterized in that: The modified polyurethane biocarrier has a specific surface area ≥800 m². 2 / g, the modified polyurethane biocarrier is a porous network structure with a porosity of 80%~90%, and the modified polyurethane biocarrier is attached with denitrifying functional bacteria.

3. The ammonia nitrogen and low-carbon treatment system for a high-density aquaculture recirculating aquaculture system according to claim 1, characterized in that: The Sn-doped TiO2 / CNTs composite catalyst coating has a Sn doping amount of 5%, and is prepared by sol-gel method and loaded onto the surface of titanium sheet electrode to form the electrode.

4. The ammonia nitrogen and low-carbon treatment system for a high-density aquaculture recirculating aquaculture system according to claim 1, characterized in that: The reaction tank is connected to a pH adjustment component, which includes a sodium bicarbonate storage tank, a metering pump, and a dosing pipeline. The metering pump is electrically connected to the PLC controller, and the outlet end of the dosing pipeline extends into the reaction tank.

5. The ammonia nitrogen and low-carbon treatment system for a high-density aquaculture recirculating aquaculture system according to claim 1, characterized in that: The ultraviolet lamp has a wavelength of 254nm and a power of 50W. The ultraviolet lamp and the electrode are arranged alternately in the photoelectrocatalytic reactor.

6. The ammonia nitrogen and low-carbon treatment system for a high-density aquaculture recirculating aquaculture system according to claim 1, characterized in that: A liquid level sensor is installed inside the buffer tank, and the liquid level sensor is electrically connected to the PLC controller.

7. The ammonia nitrogen and low-carbon treatment system for a high-density aquaculture recirculating aquaculture system according to claim 1, characterized in that: The carbon source dosing component uses a special composite carbon source made of glucose and polyhydroxyalkanoate, with a mass ratio of glucose to polyhydroxyalkanoate of 3~5:

1.

8. A method for low-carbon ammonia nitrogen treatment in a high-density aquaculture recirculating aquaculture system, implemented using the low-carbon ammonia nitrogen treatment system for a high-density aquaculture recirculating aquaculture system as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Aquaculture water circulation introduction: The high ammonia nitrogen aquaculture water in the aquaculture pond is introduced into the reaction tank at a circulation rate of 50~80% / h. The ammonia nitrogen concentration of the influent is detected in real time by an online ammonia nitrogen monitor. The PLC controller automatically calculates the carbon source addition amount according to the detection data and the formula: addition amount = ammonia nitrogen concentration × carbon-nitrogen ratio × water flow rate. S2 and SND simultaneous nitrification and denitrification treatment: The carbon source addition component adds a special composite carbon source of glucose and polyhydroxyalkanoate into the reaction tank according to the instructions of the PLC controller, controlling the carbon-nitrogen ratio in the reaction tank to be 8~12:

1. At the same time, the aeration system maintains the dissolved oxygen concentration in the reaction tank at 2~4 mg / L. The denitrification functional bacteria attached to the modified polyurethane biological carrier achieve simultaneous nitrification and denitrification of ammonia nitrogen, initially removing ammonia nitrogen from the water body, with an initial removal rate of more than 85%. S3, Real-time pH control: During the SND synchronous nitrification and denitrification process, the pH sensor monitors the acidity and alkalinity of the water in the reaction tank in real time. When pH < 7.5, the PLC controller controls the pH adjustment component to add sodium bicarbonate to the tank. S4. Photoelectrocatalytic deep treatment: The water treated by the SND biological denitrification unit is temporarily stored in a buffer tank, and then introduced into the photoelectrocatalytic reactor at a uniform speed. An external bias voltage of 0.8~1.2V is applied to the Sn-doped TiO2 / CNTs composite catalyst coating electrode, and a 254nm ultraviolet lamp is turned on. Through the synergistic effect of the Sn-doped TiO2 / CNTs composite catalyst and ultraviolet light, the residual ammonia nitrogen and recalcitrant organic matter in the water are deeply oxidized, reducing the residual ammonia nitrogen to below 0.1mg / L. S5. Purified water return: The water that has undergone photoelectrocatalytic deep treatment is directly returned to the aquaculture pond through a return pump, completing the circulation and purification of the aquaculture water.

9. A method for low-carbon ammonia nitrogen treatment in a high-density aquaculture recirculating aquaculture system according to claim 8, characterized in that, In S1, the concentration of ammonia nitrogen in the influent fluctuates within the range of 1~5 mg / L.

10. A method for low-carbon ammonia nitrogen treatment in a high-density aquaculture recirculating aquaculture system according to claim 8, characterized in that, In S2, the hydraulic retention time in the reaction tank is 4~6h; In S4, the hydraulic residence time in the photoelectrocatalytic reactor is 1~2h.

Images