System and method for treating aquaculture tail water

Abstract

The invention provides a system and a method for treating aquaculture tail water, the system comprises an electric flocculation device and a mud-membrane symbiotic reaction device, the electric flocculation device adopts an aluminum electrode, polyurethane foam is added into the mud-membrane symbiotic reaction device as a filler, a mechanical stirrer is arranged at the top of the mud-membrane symbiotic reaction device, and the mechanical stirrer is connected with the electric flocculation device. Air stones are placed at the bottom for aeration through an air pump. When the system treats tail water, the aquaculture tail water enters the electric flocculation device for pretreatment; according to the method, the final effluent turbidity is stabilized at about 2.7 NTU, the PO43-P is lower than the detection limit, the COD removal rate is 88.0%-95.8%, the TN later-stage removal rate is increased to 75.1%-81.2%, through the collaborative design of 'EC precise pretreatment + IFAS mud-membrane symbiosis', the treatment efficiency is greatly improved, and the treatment cost is reduced. The technical effects of full removal of pollutants, full adaptation of scenes, low and controllable cost and high ecological safety are achieved.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture water treatment engineering, and more specifically, relates to a system and method for treating aquaculture wastewater. Background Technology

[0002] Recirculating aquaculture systems (RAS) are a high-density method based on the recycling of aquaculture water, enabling the efficient, green, and sustainable comprehensive utilization of natural resources. The key to the stable operation of RAS lies in the efficient treatment of aquaculture wastewater. After the feed is metabolized by fish, uneaten feed and feces continuously transform into nutrients and form suspended particulate matter, directly threatening the healthy growth of farmed organisms. In RAS, aquaculture wastewater mainly includes particulate matter from feces and uneaten feed, as well as harmful substances such as ammonia, nitrates, nitrites, and phosphates. In particular, the accumulation of suspended particulate matter degrades water quality, leading to adverse effects such as gill damage, reduced disease resistance in fish, and increased biochemical oxygen demand. Therefore, reducing suspended particulate matter and turbidity in the water is essential for improving water quality.

[0003] Given the high content of suspended particulate matter such as uneaten feed and feces, as well as the high nitrogen and phosphorus nutrient salinity in aquaculture wastewater, it can be treated using biological, physicochemical, and electrochemical methods. Biological methods are highly efficient at removing dissolved organic matter and nutrients, but they typically have drawbacks such as requiring large land areas and having limited effectiveness in removing suspended solids. Physicochemical methods can treat pollutants in aquaculture wastewater with high removal efficiency, but their main disadvantages are high operating costs and the potential for secondary pollution from chemical sludge. In other words, existing biological, physicochemical, and electrochemical technologies used for treating conventional domestic wastewater cannot meet the treatment needs of aquaculture wastewater.

[0004] For example, the existing technology CN101269863B's core is a coupling technology of electrocoagulation and membrane bioreactor (MBR). It uses an iron / aluminum plate as the anode, electrolyzing to generate metal hydroxides for phosphorus removal, while simultaneously relying on microorganisms within the MBR to degrade organic matter. Its goal is to treat conventional wastewater from government offices and residential areas, with the effluent used for reclaimed water and landscaping. However, when this device is directly used to treat aquaculture wastewater, a large amount of 1-200μm residual feed / feces particles in the wastewater will deposit on the biofilm surface, causing blockage of the packing material, reducing mass transfer efficiency and the effective surface area for biofilm growth. Increasing the backwashing frequency will lead to a surge in operating costs. The high salinity of aquaculture wastewater accelerates electrode corrosion, shortens electrode life, and the high Cl- content further exacerbates the problem. - Will with Al 3+ / Fe 3+ Competition for floc adsorption sites leads to a sharp drop in phosphorus removal efficiency.

[0005] The existing technology CN120794240A is a coupling technology of electrocoagulation + AOA-type MBBR (moving bed biofilm reactor) + gravity-driven ceramic membrane MBR, targeting rural domestic sewage. It uses gravity drive to reduce energy consumption, AOA process to reduce carbon source addition, and ceramic membrane to extend lifespan and mitigate membrane fouling. However, in aquaculture effluent, a large amount of 1-200μm residual feed / feces particles adhere to the surface of the packing material, leading to biofilm hypoxia and necrosis, and reducing TN removal rate from the theoretical value to below 40%. This patent relies on the "stable carbon source" of rural domestic sewage, while the carbon source of aquaculture effluent fluctuates greatly (changes in residual feed dosage cause COD to fluctuate between 150-300mg / L). The AOA process cannot stably utilize the internal carbon source, resulting in a sharp drop in denitrification efficiency. Gravity drive is not suitable for high-density aquaculture. The water circulation in factory-style recirculating aquaculture (RAS) relies on water pumps, and gravity drive cannot be adapted to closed circulation systems. Furthermore, the ceramic membrane has limited ability to retain high suspended solids in aquaculture effluent, making it difficult to meet the effluent turbidity requirements.

[0006] The existing technology CN118289969A is based on a multi-stage unit system to share the treatment load. Targeting the characteristics of kitchen wastewater with high organic concentrations and abundant carbon sources, it achieves step-by-step removal of pollutants by sequentially setting up multiple treatment units, including an oil-water separation and conditioning pretreatment tank, an ozone-enhanced electrocoagulation tank, a biological nitrogen and phosphorus removal tank, a mud-film symbiotic enhanced treatment tank, a sedimentation tank, and an ozone oxidation filtration tank. However, if this multi-unit coupled system is directly applied to aquaculture wastewater treatment, the pretreatment units such as the conditioning tank and ozone-enhanced electrocoagulation tank, along with the multi-stage biological process, will excessively consume the already scarce dissolved organic matter in the wastewater. This results in a lack of necessary electron donors for the subsequent denitrification process, limiting denitrification efficiency and forcing the system to heavily rely on external carbon sources to maintain operation. From an economic perspective, aquaculture wastewater treatment has stringent cost control requirements. Applying this technology to aquaculture wastewater treatment not only results in a large land area and high infrastructure investment but also creates significant process redundancy when treating low-concentration wastewater, making it difficult to meet the actual application needs of the aquaculture industry.

[0007] Therefore, developing a technology for treating aquaculture water bodies that has a high pollutant removal rate, low cost, ecological safety, and small footprint is an urgent problem to be solved. Summary of the Invention

[0008] This invention is based on an advanced aquaculture wastewater treatment technology that couples electrocoagulation (EC) with integrated immobilized membrane activated sludge (IFAS). EC removes suspended solids and protects the IFAS biofilm, while IFAS degrades COD and TN that EC cannot remove. Simultaneously, trace amounts of Al remaining in the EC effluent are eliminated. 3+ It can promote sludge floc formation and improve sludge-water separation. It can reduce turbidity and PO4 in aquaculture wastewater. 3-The system achieves efficient and synergistic removal of P, COD, and TN, while simultaneously improving system stability, reducing operating costs, and meeting the wastewater purification needs of recirculating aquaculture systems (RAS).

[0009] Specifically, the system for treating aquaculture wastewater according to the present invention includes an electrocoagulation device (EC) and an in-situ symbiotic reactor (IFAS).

[0010] Furthermore, the electrocoagulation device uses aluminum electrodes with a surface area ratio of 6-7 m² / m³. The use of aluminum electrodes as sacrificial anodes in the electrocoagulation device allows for the in-situ release of Al metal cations. 3+ , with OH in water - The reaction produces hydroxide coagulants such as Al(OH)3, which remove suspended particulate matter (such as uneaten feed and fecal debris) and phosphates (PO4) from the effluent through adsorption and surface capture. 3- -P); The electrocoagulation device includes a DC regulated power supply, an plexiglass reactor, aluminum electrode plates, and a magnetic stirrer. During operation, the treatment effect is adjusted by controlling parameters such as current density and reaction time.

[0011] Furthermore, the sludge film symbiotic reaction device is equipped with polyurethane foam as filler, with a filling rate of 15-20% and a suspended sludge concentration of 3400-3600 mg / L.

[0012] Furthermore, MutagBioChip30 polyurethane foam filler was added to enrich microorganisms.

[0013] Furthermore, porous polyethylene biocarriers are used to replace polyurethane foam fillers, with the filling rate adjusted to 20-25%.

[0014] Furthermore, the sludge-film symbiotic reactor is equipped with a mechanical mixer at the top and air stones at the bottom, which are aerated by an air pump. The sludge-film symbiotic reactor combines the traditional activated sludge process with a fixed biofilm process. Biomass carriers (such as polyurethane foam packing) are added to the reactor to enrich microorganisms and form a biofilm, while suspended sludge is used to degrade pollutants. The process controls the dissolved oxygen (DO) concentration through intermittent aeration to achieve the removal of organic pollutants (COD) and total nitrogen (TN). The sludge-film symbiotic reactor includes an acrylic glass reactor, a mechanical mixer, an aeration device, and biological packing.

[0015] Furthermore, the aforementioned mud-film symbiotic reactor operates using an intermittent water intake method. The operating cycle is 8 hours, with 3 cycles per day, comprising four stages: water intake (5 minutes), reaction (6 hours), sedimentation (90 minutes), and drainage and idle (25 minutes). Furthermore, when the suspended solids concentration in the aquaculture wastewater is <50 NTU, a simple sedimentation tank (15 minutes retention time) can be added between the EC and IFAS to further reduce the turbidity of the IFAS influent and decrease the risk of biofilm fouling.

[0016] The mud-film symbiotic reactor uses intermittent aeration during the reaction stage, which more precisely matches the nitrification and denitrification needs of aquatic wastewater than timed aeration, thus avoiding energy waste.

[0017] This invention also protects a method for treating aquaculture wastewater using a system as described above, comprising the following steps: Step (1): Aquaculture wastewater enters the electrocoagulation device for pretreatment; Step (2): The pretreated supernatant enters the mud-film symbiotic reaction device for deep purification.

[0018] The electrocoagulation device pretreatment in this application removes more than 90% of particulate matter, significantly reducing the biological treatment load of the mud-film symbiotic reactor. At the same time, the "suspended sludge + biofilm" symbiotic structure (polyurethane foam packing + suspended sludge) of the mud-film symbiotic reactor is more adaptable to the carbon source fluctuations in aquatic effluent than the single suspended sludge of MBR and the single biofilm of MBBR, and the TN removal rate is greatly improved.

[0019] Furthermore, before using the electrocoagulation device in step (1), the electrode plate was soaked in 0.1M hydrochloric acid solution for 20 minutes, and the surface was polished with 1500-grit sandpaper and rinsed with pure water to eliminate the influence of the oxide layer on the electrode surface on subsequent experiments. New electrodes with polished surfaces were used for each factor investigation experiment.

[0020] Further, in step (1), the anode and cathode of the electrocoagulation device are arranged alternately in parallel and placed vertically in the center of the reactor to form a single-pole parallel circuit; the current density is 15~90A / m², the reaction time is 0~60min, the salinity is 0~30‰, and the stirring speed is 200~500rpm. An appropriate amount of nutrients is added to meet the needs of microbial growth, and the magnetic stirrer continuously stirs the electrocoagulation solution to promote the diffusion and flow of electrolytes in the reactor.

[0021] Furthermore, each operating cycle of the mud-film symbiotic reactor in step (2) includes the water intake stage, the reaction stage, the sedimentation stage, and the drainage and idle stage.

[0022] Furthermore, in step (2), sodium bicarbonate is added to supplement alkalinity before the operation of the mud-film symbiotic reaction device, so that the pH of the reactor reaction process is maintained at 7.0~7.6. Nutrients are added to meet the needs of microorganisms, with 150~200μL of nutrient salt added each time.

[0023] Compared with the prior art, the beneficial effects of the present invention are: (1) Highly efficient and comprehensive pollutant removal: The final effluent turbidity is stable at approximately 2.7 NTU, and PO4 content is low. 3- -P is below the detection limit, COD removal rate is 88.0%-95.8%, and TN removal rate is increased to 75.1%-81.2% in the later stage, meeting the requirements for reuse or discharge of aquaculture wastewater; (2) Strong system stability: EC pretreatment removes suspended solids and avoids clogging of IFAS packing material; after 18-40 days of operation, the microorganisms in IFAS adapt to the EC effluent environment, and the INT-ETS activity increases from 355 mgINTF / (gTSS·h) to 677.3 mgINTF / (gTSS·h), enhancing the shock resistance. (3) Excellent economic performance: There is no need to add a post-treatment unit for EC. IFAS reduces energy consumption through "short-frequency aeration switching" (mode V); biofilm has higher species diversity than suspended sludge, and there is no need to frequently replace packing or add chemical agents, thus reducing operating costs. (4) Synergistic mechanism of EC and IFAS: EC removes suspended solids to protect the IFAS biofilm, while IFAS degrades COD and TN that EC cannot remove. At the same time, trace amounts of Al remain in the EC effluent. 3+ It can promote the formation of sludge flocs and improve the sludge-water separation effect; (5) This invention constructs a simplified treatment system consisting of only two core units: electrocoagulation (EC) and biofilm symbiosis (IFAS). The front-end EC unit serves as a precise pretreatment, efficiently retaining over 90% of suspended particulate matter and completely eliminating the risk of packing blockage, while avoiding the unnecessary consumption of organic matter in the water by strong oxidation processes. This maximizes the retention of essential dissolved carbon sources (such as residual feed leaching) for the subsequent IFAS unit. The back-end IFAS unit, with its "suspended sludge + biofilm" structure combined with intermittent aeration, fully utilizes the retained native carbon sources under low carbon-to-nitrogen ratio stress, achieving efficient pollutant degradation and saving energy. This simplified configuration not only reduces dependence on external carbon sources and avoids the use of energy-intensive deep oxidation and complex recirculation components, but also reduces the treatment cost per unit of water, thus achieving both high technical efficiency and stability, and low cost and controllability in aquaculture wastewater purification. (6) This application is a “customized technology” specifically developed for aquaculture wastewater. Through the synergistic design of “EC precision pretreatment + IFAS mud film symbiosis”, it achieves “complete removal of pollutants, full adaptation to scenarios, low cost and controllable cost, and high ecological safety”, which is a more suitable technical solution for treating aquaculture water bodies. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the electrocoagulation test device of the present invention; Figure 2 This is a schematic diagram of the IFAS process apparatus of the present invention; Figure 3 The interaction response surface diagrams between the parameters of current density, reaction time, salinity, and stirring speed of this invention are: a) reaction time × current density; b) salinity × current density; Figure 4 This is a response surface diagram showing the interaction between the parameters of reaction time, salinity, and stirring speed in this invention: a) stirring speed × current density; b) reaction time × salinity; Figure 5 The interaction response surface diagrams of the parameters current density, reaction time, salinity, and stirring speed of this invention are: a) reaction time × stirring speed; b) stirring speed × salinity; Figure 6 This is a graph showing the change in INT-ETS activity during the operation of the electrocoagulation-mud film symbiosis process in Example 2; Figure 7 During the operation of the electrocoagulation-mud film symbiotic process in Example 2, the pollutants (a) turbidity removal in the coupled system; (b) PO4 removal in the coupled system. 3- -P removal status; Figure 8 The pollutant removal status during the operation of the electrocoagulation-mud film symbiosis process in Example 2 is as follows: (a) COD removal by the IFAS system; (b) TN removal by the IFAS system. Figure 9 The pollutants during the operation of the electrocoagulation-mud film symbiosis process in Example 2 are: (a) C / N ratio of the IFAS influent; (b) changes in IFAS pollutant concentrations during the cycle. Figure 10 This refers to the relative abundance of bacteria at the phylum level on the biofilm attached to the suspended sludge and packing material during the operation of the electrocoagulation-mud film symbiosis process in Example 2. Figure 11 It is the relative abundance of bacteria at the genus level on the biofilm attached to the suspended sludge and packing material during the operation of the electrocoagulation-mud film symbiosis process in Example 2. In the diagram, 1-DC regulated power supply; 2-electrode wire; 3-aluminum electrode plate; 4-test water sample; 5-magnetic stirring device; 6-EC effluent storage tank; 7-electric mixer; 8-mud film symbiotic reactor; 9-aeration device; 10-IFAS effluent storage tank. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only, representing schematic diagrams rather than actual physical objects, and should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0026] The detection indicators involved in the following examples include NH4 + -N, NO2 - -N, NO3 - -N,PO4 3- -P, COD, DO, etc., the specific detection methods are shown in Table 1.

[0027] Table 1 Detection Methods

[0028] The specific testing equipment names and models involved in the testing methods are shown in Table 2.

[0029] Table 2. List of Main Instruments and Equipment

[0030] Example 1

[0031] This embodiment provides a system for treating aquaculture wastewater (EC-IFAS system), such as Figure 1 As shown, the system includes an electrocoagulation (EC) device and an in-situ symbiotic (IFAS) reactor. The electrocoagulation device includes a DC regulated power supply 1, electrode wires 2, an aluminum electrode plate 3 (100mm long × 100mm wide × 3mm thick), a magnetic stirring device 5, and an acrylic reactor (13cm long × 12cm wide × 20cm high, volume 2.5L, not shown in the figure). The aluminum electrode plate 3 is immersed 6.5cm below the liquid surface, with an effective working area of ​​65cm², and a surface-to-volume ratio of 6.5m² / m³. The anode and cathode of the electrocoagulation device are arranged alternately in parallel and vertically at the center of the reactor, forming a single-pole parallel circuit.

[0032] like Figure 2As shown, the IFAS (Integrated Foil Bioreactor) includes an EC effluent storage tank 6, an electric mixer 7, an IFAS reactor 8 (13 cm in diameter, 30 cm in height, with a working volume of 2.75 L), an aeration device 9, and an IFAS effluent storage tank 10. The IFAS reactor 8 contains both biofilm packing material and suspended sludge. MutagBioChip30 polyurethane foam is added as the biofilm packing material, with a filling rate of 20% and a suspended sludge concentration of 3500 mg / L. The IFAS reactor 8 is equipped with an electric mixer 7 at the top, and the aeration device 9 uses an air pump to aerate the sludge by placing air stones at the bottom.

[0033] Example 2 This embodiment provides a method for treating aquaculture wastewater using the system for treating aquaculture wastewater described in Embodiment 1, comprising the following steps: Step (1) Before using the electrocoagulation device, the aluminum electrode plate is soaked in 0.1M hydrochloric acid solution for 20 minutes, and the surface is polished with 1500-grit sandpaper and rinsed with pure water. Step (2) Aquaculture wastewater (Aquaculture wastewater quality: TN 55mg / L, NH4) + -N 45mg / L, PO4 3- -P3mg / L, turbidity 110NTU) was used as experimental water sample 4 and pretreated in the electrocoagulation device; the DC regulated power supply 1 output current density of 60.2A / m², reaction time of 35.7min, salinity of 0.65‰ (the salinity was adjusted by sea crystal and measured by a salinity meter (BLE-C600, Shenzhen Hengchi Yuanchuang Technology Co., Ltd.)), and magnetic stirring speed of 258rpm were optimized by response surface methodology (RSM) to balance turbidity / PO4. 3- -P removal rate and energy consumption; Step (3) The pretreated supernatant is put into the mud film symbiotic reactor and run continuously for 40 days for deep purification; the supernatant is obtained by natural sedimentation for 30 minutes after each electrocoagulation; specifically, 1L of supernatant is placed in EC effluent storage tank 6, and the supernatant is pumped into mud film symbiotic reactor 8 for 5 minutes. After the reaction is completed, the supernatant is output to IFAS effluent storage tank 10.

[0034] The mud-film symbiotic reactor operates with an intermittent water intake method, with an 8-hour operating cycle and three cycles per day, comprising four stages: water intake (5 min), reaction (6 h), sedimentation (90 min), and drainage and idle (25 min). During the reaction stage, the mud-film symbiotic reactor uses intermittent aeration to ensure alternation between aerobic and anoxic phases. In the 6-hour reaction period, the first 5 hours alternate between 25 min of aerobic aeration and 35 min of anoxic aeration, followed by 1 hour of anoxic aeration. Aeration is activated during the aerobic period at a rate of 2 L / min. The electric mixer 7 starts simultaneously with the start of the reaction after each water intake cycle and stops after the 6-hour reaction period, maintaining a constant stirring speed of 80 rpm / min.

[0035] The Response Surface Method (RSM) employed the Box-Behnken method to construct a four-factor, three-level design. Reaction time (X1), current density (X2), salinity (X3), and stirring speed (X4) were used as independent variables. Three levels were selected for each factor and coded as (-1, 0, 1). The turbidity removal rate of aquaculture wastewater was used as the response quantity. Regression equations were fitted to 27 experimental groups, and response surface analysis was performed using Design-Expert 13 software. Factor levels and coding are shown in Table 3, and the response surface experimental design and results are shown in Table 4.

[0036] Table 3. Levels and Codings of Response Surface Design Factors

[0037] Table 4 Response Surface Experimental Design and Results

[0038] RSM 3D surface plot as follows Figure 3 , Figure 4 as well as Figure 5 As shown in (a) and (b), this figure graphically represents the interaction of two variables with respect to the response when other variables remain constant. Figure 3 (a) shows the effect of reaction time and current density on turbidity removal efficiency. When the current density is in the range of 60-70 A / m² and the reaction time is close to 30 min, the response surface shows a significant convex feature, corresponding to the highest removal efficiency. However, as the current density and reaction time continue to increase, the surface tends to flatten or even slightly decrease. This may be due to excessive electrolysis leading to an intensified flotation effect or floc breakage, which reduces the solid-liquid separation efficiency. Figure 3As shown in (b) and 4(a), the interaction between current density, salinity, and stirring speed is not significant. When salinity is constant, the turbidity removal rate gradually increases with increasing current density, while when current density is constant, the turbidity removal rate increases with decreasing salinity. When salinity increases, the amount of Cl- in the water increases. - Concentration will occupy the active sites on the surface of Al(OH)3 flocculant, competing with suspended particles and colloidal particles in the water for adsorption, leading to a decrease in flocculation efficiency; at a stirring speed of 260-300 rpm and a current density of 60 A / m 2 Under these conditions, the response value reaches its peak, indicating that a moderate stirring speed can ensure a good balance between mass transfer and floc growth. However, a significant increase in stirring speed reduces the floc formation capacity, thereby reducing the EC removal efficiency. The interactions between reaction time and salinity, and between reaction times themselves, are as follows: Figure 4 As shown in (b) and 5(a), in both cases, the increase in reaction time is beneficial to the improvement of removal efficiency, which indicates that a longer reaction time helps to form more hydroxides, and the removal of pollutants is mainly proportional to the reaction time. Figure 5 (b) shows the interaction between stirring speed and salinity. When the salinity is constant, the turbidity removal rate first increases and then decreases with the increase of stirring speed. When the stirring speed is constant, the turbidity removal rate increases with the decrease of salinity. When the stirring speed is 200 rpm, the turbidity removal rate increases from 85.2% to 90.95% when the salinity decreases from 1.5‰ to 0.5‰.

[0039] Furthermore, the optimal value was predicted using the Numerical option within the Optimization function of the Design-Expert 13 software, with a current density of 30 A / m selected. 2 ~90A / m 2 The reaction time was 20–40 min, the salinity was 0.5‰–1.5‰, and the stirring speed was 200 rpm–320 rpm. The optimal conditions were determined to be 60.2 A / m. 2 The current density, reaction time of 35.7 min, salinity of 0.65‰, and stirring speed of 258 rpm were used.

[0040] INT-ETS was used to characterize sludge activity. Iodonitrostetrazol (INT) is a commonly used electron acceptor for detecting the ETS (electron transport system) of activated sludge. After being added, it accepts electrons through the electron transport system of microorganisms and is reduced to INTF, becoming a red substance that is easily detected.

[0041] The specific method for determining INT-ETS activity is as follows: Take 0.6 mL of sludge mixture and place it in a 15 mL centrifuge tube. Add 3 mL of Tris-HCl buffer solution and 2 mL of 0.2% INT solution. Quickly place the prepared sample in a water bath shaker at (37±1)℃ and shake for 30 min. Then add 2 mL of 37% formaldehyde to terminate the enzyme reaction. Centrifuge the sample at 4000 r / min for 5 min, gently discard the supernatant, add 10 mL of acetone, stir and mix well, and continue to extract in the dark at (37±1)℃ for 30 min. After the sample extraction is complete, centrifuge again at 4000 r / min for 5 min to separate the supernatant and the precipitated sludge. Read the absorbance of the extract at 485 nm using a spectrophotometer. After drying the centrifuged precipitated sludge at (105±1)℃ for 1 h, measure the dry weight. The formula for calculating INT-ETS activity is as follows: ; Where: UT: INT-ETS activity, mgINTF / (gTSS·h); D485: Absorbance of the supernatant at a wavelength of 485 nm; V: Extractant volume, mL; K: Slope of the standard curve, L / mg; W: Sludge dry weight, mg; T: Incubation time, h.

[0042] During the operation of the EC-IFAS system, the mixed liquor in the sludge film co-production reactor 8 was taken as a sample, and the suspended sludge in it was collected as the target for INT-ETS activity determination to characterize the electron transport system activity of suspended microorganisms in the system. Figure 6 The results of INT-ETS activity measurement within 40 days of EC-IFAS system operation are as follows: In the initial stage of operation (day 8), the INT-ETS activity was 355.5 mg INTF / (gTSS·h), and the TN removal rate was 40.4%. The effluent TN concentration was relatively high, mainly NO3. - -N was the dominant form, indicating that nitrification had been largely achieved, while denitrification contributed relatively little. At this stage, INT-ETS activity was at a low level, corresponding to the gradual establishment of the overall electron transfer rate and microbial metabolic activity of the system. By day 16, INT-ETS activity increased to 384.7 μg INT / (g TSS·h), TN removal rate increased to 49.3%, and effluent NO3... -The nitrogen-12O (TN) concentration decreased, but remained the main form of total nitrogen (TN), indicating that while the microbial metabolic level increased, the denitrification capacity gradually improved. By day 24, the INT-ETS activity rose to 521.1 mg INTF / (gTSS·h), an increase of 46.6% compared to day 8. At this point, the TN removal rate increased to 74.0%, and the effluent NO3... - The simultaneous decrease in NO3- and TN concentrations indicates a significant enhancement in the nitrogen conversion rate within the system. The increasing trend of INT-ETS activity is consistent with the change in TN removal rate. On day 32, the INT-ETS activity reached 671.5 mg INTF / (gTSS·h), and the TN removal rate was 81.2%, the highest value during operation. - The concentrations of -N and TN remained at low levels, indicating that the system's nitrogen removal performance had entered a stable phase. By day 40, the INT-ETS activity was 677.3 mg INTF / (gTSS·h), essentially the same as on day 32, and the TN removal rate remained stable at 80.1%. The effluent NO3... - The concentrations of -N and TN fluctuated relatively little. The phased increase in INT-ETS activity was consistent with the increase in TN removal rate, reflecting that the system's microbial respiration intensity and nitrogen conversion capacity gradually increased and tended to stabilize during operation.

[0043] like Figure 7-9 As shown, during the 40-day operation, the coupled EC–IFAS system exhibited changes in turbidity and PO4. 3- It exhibits excellent treatment performance and good operational stability in both P and COD removal. The average influent turbidity of the simulated aquaculture wastewater is 112 NTU. Figure 7 (a) After EC pretreatment, the turbidity was effectively reduced to 7-8 NTU. Subsequently, the retention and filtration effects of suspended sludge flocs and biofilm packing in the IFAS reactor further promoted turbidity removal, resulting in an average effluent turbidity of 2.7 NTU and a total turbidity removal rate of 97.6%. For PO4... 3- -P, with an average influent concentration of 3.5 mg / L, was reduced to below 0.1 mg / L after EC treatment, and further reduced to below the detection limit in the IFAS effluent. Figure 7 (b)).

[0044] Meanwhile, the COD concentration in the EC effluent remained stable at 216 mg / L, and the IFAS reactor achieved a COD removal rate of 91.9%. Figure 8 (a)). For example, Figure 8 As shown in (a), during the initial 0–16 days of operation, the average TN removal rate of the IFAS reactor was 40.4%–55.8%. (Effluent NH4) + -N concentration is comparable to the results of the operation mode optimization phase. Figure 8(b)) Almost complete removal is achieved at the end of each running cycle.

[0045] The average concentration of total nitrogen (TN) in the IFAS effluent was 27.72 mg / L, mainly in the form of NO3. - The TN removal rate was limited during the initial operation period (0-16 days) due to the following reasons: the average total aluminum concentration in the EC effluent was 28 mg / L, mainly derived from aluminum flocs generated during anodic dissolution but not completely settled and separated. Although dissolved Al in the EC effluent... 3+ The concentration was low (average 0.2 mg / L), but residual aluminum flocs entering the IFAS unit may continue to release trace amounts of Al. 3+ These released Al 3+ It is believed to have a chronic inhibitory and toxic effect on the enzyme systems of nitrifying and denitrifying bacteria. Specifically, Al 3+ It may disrupt the structural integrity of bacterial cell walls, interfere with the transmembrane transport of nutrients and metabolites, damage the cytoplasmic membrane, and affect various intracellular metabolic processes. These adverse effects collectively lead to the obstruction of nitrogen metabolism pathways. At lower Al levels... 3+ At a concentration (10 mg / L), COD, TN, and NH4+ in the aerobic zone + The removal rates of -N increased by 5.5%, 7.1%, and 34.7%, respectively; however, at higher concentrations (40 mg / L), it showed a significant inhibitory effect, with COD and TN removal rates in the aerobic zone decreasing by 33.8% and 21.4%, respectively.

[0046] During the initial operation phase (0-16 days), the IFAS unit was affected by residual Al in the EC effluent. 3+ The impact of [unspecified factor] suppressed TN removal efficiency, but TN removal performance gradually recovered in the subsequent operation phase (18-40 days). During the 18-28 day operation phase, the TN removal rate increased to 70.6%-77.4%, and the effluent NO3 [unspecified factor] [unspecified factor]. - -N concentration dropped below 15 mg / L. After 30-40 days of operation, TN removal rate further increased to 75.1%-81.2%, exceeding the highest level in the previous operation mode optimization phase, corresponding to effluent NO3... - -N concentration remained stable between 9.86 and 12.96 mg / L.

[0047] Traditional complete denitrification theoretically requires a high C / N ratio (usually greater than 5), such as Figure 9 As shown in (a), the C / N ratio of the EC effluent in this application is at a relatively low level of 3.5-4.9, indicating that the carbon source of the system is relatively limited. Under these conditions, the IFAS reactor can achieve a high COD removal rate and a stable increase in the TN removal rate in the later stage. Figure 9(b) This shows the changes in pollutant concentrations within a single operating cycle (0–360 min) of the IFAS system under stable operating conditions. NH4 + The NO-N concentration initially decreased rapidly from 46.35 mg / L to 28.78 mg / L due to dilution by the reactor mixture, then further decreased to 12.3 mg / L within 0–120 min, and was completely removed at 240 min. Meanwhile, NO3- - -N concentration fluctuates periodically with alternating aeration / non-aeration operation of the reactor. Throughout the entire operating cycle, NO2... - The -N concentration remained below 0.3 mg / L, and no significant nitrite accumulation was observed. The TN concentration continuously decreased from 51.86 mg / L to 12.45 mg / L, indicating that the simultaneous nitrification-denitrification (SND) process in the reactor was effectively carried out.

[0048] like Figure 10 As shown, the relative abundance of bacteria at the phylum level on suspended sludge and biofilms attached to the packing material in the IFAS device at different stages was analyzed. S0–S3 represent suspended sludge samples, and M1–M3 represent biofilm samples on the packing material surface, all derived from microbial samples at the corresponding stages of IFAS device operation. S0 is the inoculum sludge added at reactor startup (i.e., the original activated sludge used to start the reactor); S1, S2, and S3 are suspended sludge samples collected from the reactor mixed liquor during IFAS device operation (0 d, 14 d, and 40 d); M1, M2, and M3 are attached biofilm samples collected from the surface of the reactor packing material at the same stage. Sample collection, total DNA extraction, PCR amplification, amplicon library construction, and sequencing on the Illumina platform were performed. Bioinformatics analysis of the microbial 16S rRNA gene sequences yielded taxonomic information on the microorganisms in the samples, including different taxonomic levels such as phylum, class, order, family, and genus.

[0049] Proteobacteria (Proteobacteria) and Bacteroidota Bacteroidetes are the dominant bacterial phylum in suspended sludge and biofilm within the IFAS unit. Proteobacteria It had the highest abundance among all samples (except S1), and its abundance in M1, M2, and M3 was all above 50%, which was higher than that of suspended sludge at the same stage. Proteobacteria Widely found in wastewater, it can degrade extracellular polymers and is also a type of bacteria that aids in nitrification and denitrification. Bacteroidota They are heterotrophic bacteria responsible for the degradation of organic matter, after optimization of the IFAS operating mode (before the coupled process). BacteroidotaThe abundance in S0 increased from 24.90% to 45.91% in S1. This is because intermittent aeration and the more refined switching frequency of hypoxic / aerobic environments created periodic hypoxic microzones. Bacteroidota As facultative anaerobic bacteria, their abundance increased significantly, and M1, M2, and M3 also showed increased abundance. Bacteroidota The relative abundances of the three groups were 30.4%, 13.9%, and 29.05%, respectively. This trend is consistent with the trend described in Section 4.3.1, where the average TN removal efficiency decreased to 46.5% after the start of the coupling process and then increased to 78.2%, while the effluent NO3... - This is consistent with the decrease in the average concentration of -N from 26.37 mg / L to 11.41 mg / L. Chloroflexi (Aureobacteria) is an important bacterial group that can form sludge flocs and degrade recalcitrant organic matter. Its relative abundance increased from 1.93% in S1 to 3.62% in S3, which is consistent with the recovery of system performance in the later stages of operation (18-40 days). Studies have reported that... Chloroflexi It contains Al 3+ The most important phylum in lake sediment microbial communities. Nitrospirota The relative abundances of (Nitrifying Spirulina) in S1, S2, and S3 were 5.88%, 0.72%, and 10.75%, respectively. Myxococcota The relative abundances of (Myxococci) in S1, S2, and S3 were 0.92%, 3.08%, and 12.1%, respectively. Nitrospirota The gate is related to ammonia removal. Myxococcota It has been identified as a potential contributor to nitrogen and phosphorus removal processes, and its metabolic activity may contribute to sludge floc formation and the maintenance of system stability. Nitrospirota and Myxococcota The increased abundance in S3 and M3 may be related to the recovery of the denitrification performance of the IFAS unit in the later stages of the coupled process operation.

[0050] Figure 11 The relative abundance of bacteria at the genus level on the suspended sludge and biofilm attached to the packing material in different stages of the IFAS device. Thauera (Daucus) and Terrimonas (Geomonas) is the dominant bacterial genus in suspended sludge and biofilm within the IFAS unit. Thauera It plays a crucial role in removing organic pollutants, nitrogen, and phosphorus, and resisting the impact of toxic pollutants. During the operation of the coupled process, suspended sludge and biofilm... Thauera The relative abundance of both S2 and M2 showed a trend of first decreasing and then increasing. Thauera Affected by the complex water quality of EC effluent, after a period of adaptation, the percentages increased from 3.9% and 10.91% to 10.81% and 14.81% for S3 and M3, respectively. TerrimonasIt is a common heterotrophic bacterium and the main denitrifying bacteria in S2 and S3, with relative abundances of 21.54% and 25.94%, respectively. This indicates that... Terrimonas It may be tolerant to residual aluminum in EC effluent, thus aiding in system recovery. Studies have shown that... Defluviimonas (Deferiorhynchus) can degrade recalcitrant organic matter; in addition, it has been reported that... Kapabacteriales (Kappa bacteria) Ferruginibacter (Genus *Aristolochia*) SWB02 Classified as denitrifying bacteria, Nitrospira (Nitrifying Spirulina) Ellin6067 They are classified as nitrifying bacteria. It is worth noting that... Ferruginibacter The relative abundance of Al decreased from 18.04% in S1 and 7.99% in M1 to 7% in S2 and 1.97% in M2, and then rebounded to 9.43% and 5.08% in S3 and M3, respectively. This is consistent with the suppression and subsequent recovery of TN removal, suggesting that denitrification in the IFAS unit may be due to Al 3+ The effects were temporarily suppressed.

[0051] In terms of particulate matter removal, this invention achieves a removal rate of ≥90% for 1-200μm particles (<40μm particles ≥90%) through RSM parameter optimization in the EC stage. Salinity adaptation: experiments have verified that a salinity range of 0.5-1.5‰ is optimal. Even when the salinity rises to 30‰, a turbidity removal rate of over 80% can be maintained by adjusting the current density (e.g., increasing from 60.2A / m² to 70A / m²), making it suitable for both seawater and freshwater aquaculture scenarios. Besides conventional COD, nitrogen, and phosphorus removal, the EC can also remove some pathogens (such as Vibrio) through floc adsorption. The IFAS biofilm can further degrade precursors of earthy odor (gestigma, 2-methylisoborneol), resulting in effluent that meets the high-end aquaculture market's requirements of "no drug residues, no earthy odor." The EC uses aluminum electrodes, and the dissolved Al... 3+ The concentration was only 0.2±0.02 mg / L, far below the safety threshold for aquaculture (1 mg / L), and the microbial community of IFAS can adapt to trace amounts of Al. 3+This design avoids toxicity to cultured organisms. After EC parameter optimization, power consumption per unit water volume is reduced by 30%. The IFAS (Integrated Fusion Aquaculture System) requires no additional carbon source (utilizing residual feed carbon sources), resulting in an operating cost of only 0.2-0.3 yuan / m³, significantly lower than the 0.5-0.8 yuan / m³ mentioned in the previous two documents, thus meeting the low-cost requirements of aquaculture. The IFAS reactor of this invention is small in size (an effective volume of 2.5L is sufficient for experimental needs and can be scaled up), and its "suspended sludge + biofilm" structure resists hydraulic shock, making it suitable for high-frequency circulation in RAS (3-6 times per day). The EC unit can be modularly designed to handle large water volumes in ponds (e.g., 1000m³). The natural ventilation aeration of the IFAS (referencing the energy-saving design of the previous two documents) reduces energy consumption in outdoor aquaculture, and the packing material is resistant to sun and rain, with a lifespan of 2-3 years.

[0052] The core objective of aquaculture is to "produce safe and high-quality aquatic products." This technology has significant advantages in ecological safety: no chemical additives are required: EC removes phosphorus by generating Al(OH)3 flocs in situ, eliminating the need for chemical flocculants such as PAC and PAM, thus avoiding the impact of drug residues on fish health; synergistic microbial community: the biofilm of IFAS and the suspended sludge form a "functional complementarity." The core functional bacteria not only improve denitrification efficiency but also inhibit the growth of pathogens (such as Vibrio) and reduce the incidence of fish diseases (no fish deaths due to water quality were observed in the experiment).

[0053] The effluent is recyclable: final effluent turbidity ≤ 2.7 NTU, PO4 3- -P≤ detection limit, TN≤12mg / L, can be directly reused in aquaculture water (the effluent from the first two documents can only be used as reclaimed water / landscape water and cannot be directly used for aquaculture), achieving "zero discharge" and meeting the needs of green transformation of aquaculture.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A system for treating aquaculture wastewater, characterized in that, The system includes an electrocoagulation device and a mud-film symbiotic reaction device.

2. The system for treating aquaculture wastewater according to claim 1, characterized in that, The electrocoagulation device uses aluminum electrodes with a surface area ratio of 6~7 m² / m³.

3. The system for treating aquaculture wastewater according to claim 1, characterized in that, The mud-film symbiotic reaction device adds polyurethane foam as filler, with a filling rate of 15-20% and a suspended sludge concentration of 3400-3600 mg / L.

4. The system for treating aquaculture wastewater according to claim 3, characterized in that, The mud film symbiotic reaction device is equipped with a mechanical mixer at the top and air stones at the bottom for aeration by an air pump.

5. The system for treating aquaculture wastewater according to claim 4, characterized in that, The mud-film symbiotic reaction device operates in an intermittent water intake mode.

6. The system for treating aquaculture wastewater according to any one of claims 1-5, and the method for treating aquaculture wastewater, characterized in that, Includes the following steps: Step (1): Aquaculture wastewater enters the electrocoagulation device for pretreatment; Step (2): The pretreated supernatant enters the mud-film symbiotic reaction device for deep purification.

7. The method according to claim 6, characterized in that, Step (1) Before using the electrocoagulation device, the electrode plate is soaked in 0.1M hydrochloric acid solution for 20 minutes, and the surface is polished with 1500-grit sandpaper and rinsed with pure water.

8. The method according to claim 6, characterized in that, Step (1) The anode and cathode of the electrocoagulation device are arranged alternately in parallel and placed vertically in the center of the reactor; the current density is 15~90A / m², the reaction time is 0~60min, the salinity is 0~30‰, and the stirring speed is 200~500rpm.

9. The method according to claim 6, characterized in that, Step (2) Each operating cycle of the mud-film symbiotic reactor includes the water intake stage, reaction stage, sedimentation stage, drainage stage, and idle stage.

10. The method according to claim 9, characterized in that, Step (2) Before the operation of the mud-film symbiotic reactor, sodium bicarbonate is added to supplement alkalinity so that the pH of the reactor reaction process is maintained at 7.0~7.6, and 150~200μL of nutrients are added.

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