A purification treatment method for realizing standard discharge of aquaculture tail water by using microbial technology

Abstract

This invention belongs to the field of aquaculture wastewater treatment technology, and discloses a purification treatment method for achieving compliant discharge of aquaculture wastewater using microbial technology. After large particulate suspended solids are removed from the wastewater by a screen, the retained uneaten feed and feces are ground into a slurry and sent together with the screen effluent into a parallel, alternating hydrolysis acidification tank. Directed acid-producing bacteria are added to convert macromolecular organic matter into volatile fatty acids as an endogenous carbon source. The effluent is then sent to a parallel, alternating immobilized biofilm reactor, where nitrogen and phosphorus are simultaneously removed by a carrier loaded with functional bacteria and an adsorption phosphorus removal module. After desorption by the saturated adsorption module, the phosphorus-rich solution is crystallized using struvite to recover phosphorus. The effluent is then ecologically stabilized and disinfected before discharge or reuse. This method eliminates the need for additional external carbon sources, reducing operating costs. Simultaneous nitrogen and phosphorus removal in a single tank reduces the process footprint. High phosphorus recovery rate avoids secondary pollution. It is adaptable to various operating conditions, including low temperature and high load, and is suitable for various freshwater aquaculture wastewater treatment scenarios.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture wastewater treatment technology, and in particular to a purification treatment method that utilizes microbial technology to achieve compliant discharge of aquaculture wastewater. Background Technology

[0002] Currently, the scale and intensification of freshwater aquaculture in my country are continuously improving, with annual wastewater discharge exceeding 30 billion tons. Excessive discharge of pollutants such as nitrogen, phosphorus, uneaten feed, and feces in wastewater is the core cause of eutrophication in river basins. The industry urgently needs wastewater treatment technologies that are low-cost, stable in operation, and capable of resource recovery to meet standards.

[0003] The current mainstream freshwater aquaculture wastewater treatment process is represented by a staged biological treatment combination process. Its working principle involves sequentially passing the wastewater through an anaerobic tank for denitrification, an aerobic tank for nitrification and a chemical flocculation tank for phosphorus removal, and finally through an ecological pond for further treatment before discharge. This technology is mature and highly adaptable to different treatment loads, and its application rate in large-scale aquaculture bases in China currently exceeds 60%. However, this process has clear drawbacks: First, the denitrification and phosphorus removal processes must be completed in separate tanks, requiring a large area. Furthermore, the denitrification process is highly dependent on exogenous carbon sources such as sodium acetate and glucose, resulting in operating costs that are more than 40% higher than processes using endogenous carbon sources. Second, chemical phosphorus removal generates a large amount of phosphorus-containing hazardous sludge, making phosphorus resource recovery impossible and posing a risk of secondary pollution.

[0004] Another mainstream technology is the algae-bacterial symbiotic treatment technology, which achieves simultaneous degradation of pollutants by constructing a synergistic system of bacteria and algae. It has low energy consumption and no secondary pollution caused by the addition of chemical agents, and is mostly used for the treatment of wastewater from small and medium-sized aquaculture farms. However, this technology has significant drawbacks: First, the nitrogen and phosphorus removal efficiency of the algae-bacterial system is greatly affected by environmental factors such as temperature and light, and the stability of effluent compliance is insufficient when water quality fluctuates; second, phosphorus removal relies on the assimilation and absorption by bacteria and algae, resulting in low phosphorus enrichment efficiency and the inability to recover phosphorus in a targeted manner. The total phosphorus removal rate in the wastewater is generally less than 60%, which is difficult to meet the Class I standard of the "Requirements for Freshwater Aquaculture Wastewater Discharge".

[0005] The existing technologies mentioned above cannot simultaneously meet the multiple requirements of carbon self-sufficiency, simultaneous nitrogen and phosphorus removal, and closed-loop phosphorus resource recovery in aquaculture wastewater. This seriously restricts the cost reduction, efficiency improvement, and resource utilization of freshwater aquaculture wastewater treatment. There is an urgent need to develop new treatment technologies that are suitable for the water quality characteristics of freshwater aquaculture wastewater. Summary of the Invention

[0006] To address the shortcomings of existing aquaculture wastewater treatment processes, such as large footprint, high carbon source costs, difficulty in phosphorus resource recovery, and poor stability in effluent compliance, this invention provides a purification treatment method that utilizes microbial technology to achieve compliant discharge of aquaculture wastewater.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A purification treatment method for achieving compliant discharge of aquaculture wastewater using microbial technology includes the following steps: S1. Pretreatment and preparation of endogenous carbon source: After the aquaculture effluent is treated by a screen to remove large particulate suspended matter, the retained residual feed and feces are ground into slurry and sent together with the screen effluent into an alternating hydrolysis acidification tank. The hydrolysis acidification tank consists of at least two sets of parallel closed tanks. Targeted acid-producing bacteria are added to the tank to convert macromolecular organic matter into volatile fatty acids, which serve as the endogenous carbon source for subsequent treatment. S2. Simultaneous nitrogen and phosphorus removal: The effluent from the hydrolysis acidification tank is sent to at least two sets of parallel immobilized biofilm reactors. The two sets of reactors are switched and operated alternately. The reactors are filled with biofilm carriers and detachable adsorption phosphorus removal modules. The biofilm carriers are immobilized with aerobic heterotrophic nitrification-denitrification bacteria. Under micro-aeration conditions, using the endogenous carbon source described in step S1, organic matter degradation, ammonia nitrogen oxidation and denitrification are completed simultaneously in the same reactor. At the same time, the phosphorus-containing tailwater flows through the adsorption phosphorus removal module to achieve phosphate enrichment. S3. Phosphorus Removal Module Regeneration and Phosphorus Recovery: When the adsorption phosphorus removal module is saturated, the saturated module is removed from the currently operating reaction tank and transferred to the regeneration unit for desorption to obtain a phosphorus-rich desorption solution. At the same time, another set of reaction tanks is switched to the operating state. The phosphorus-rich desorption solution recovers phosphorus resources through struvite crystallization reaction. The desorbed adsorption module is returned to the reaction tank for continued use after neutralization and cleaning. S4. Ecological Stabilization and Effluent: The effluent from the immobilized biofilm reactor is sent to the ecological stabilization tank. The residual nitrogen and phosphorus are removed by the adsorption and interception of composite packing and the absorption of emergent plants. The nitrogen and phosphorus are removed from the system by the harvesting of plants and the regeneration of packing. The effluent is then disinfected before being discharged or reused.

[0008] Furthermore, in step S1, the two sets of hydrolysis acidification tanks are operated alternately in a 12-24 hour cycle; the directional acid-producing bacteria agent is a composition of Clostridium butyricum, Lactococcus lactis, and Bacillus coagulans in a mass ratio of 2-3:1-2:1; the pH of the hydrolysis acidification tank is controlled at 6.0-7.5, and the hydraulic retention time is 6-12 hours; the top of the sealed tank of the hydrolysis acidification tank is equipped with a gas collection hood and a water seal device to maintain the anaerobic environment in the tank to ensure the acid-producing activity of Clostridium butyricum, and at the same time, the biogas generated in the tank is periodically discharged.

[0009] Furthermore, in step S2, the biofilm carrier is a porous polyurethane sponge or a composite fiber ball, and the adsorption phosphorus removal module is a permeable grid box with built-in modified lanthanum-based biochar; the modified lanthanum-based biochar is filled in the grid box, and the module can be independently disassembled and replaced; the filling ratio of the biofilm carrier in the reaction tank is 15%~30%, and the filling ratio of the adsorption phosphorus removal module is 10%~20%.

[0010] Furthermore, the aerobic heterotrophic nitrifying-denitrifying bacterial community mentioned in step S2 is a compound bacterial agent of Pseudomonas, Bacillus, and Alcaligenes; Chlorella is also immobilized on the surface of the biofilm carrier to form a bacterial-algal symbiotic system, and the biomass ratio of bacterial agent to Chlorella is 3~5:1; the immobilized biofilm reaction tank is equipped with a light-transmitting window or a built-in LED light source with a light intensity of 2000~5000 lux.

[0011] Furthermore, the micro-aeration described in step S2 uses microporous aeration discs, and the aeration rate is controlled by dissolved oxygen feedback to maintain the dissolved oxygen concentration in the reaction tank at 0.5~2.0 mg / L, the reaction temperature at 15~35℃, and the hydraulic retention time at 8~16h.

[0012] Furthermore, the reaction cell described in step S2 is also equipped with a microcurrent enhancement system, which includes electrodes and a power source. The electrodes are carbon felt electrodes with an electrode spacing of 1-5 cm and a current density of 0.1-1.0 mA / cm². 2 It uses DC or pulse power supply, and is powered on for 1 hour and then off for 3 hours. The microcurrent enhancement system is suitable for freshwater aquaculture wastewater with chloride ion concentration below 250 mg / L. When the chloride ion concentration is higher than 250 mg / L, the microcurrent system stops operating and nitrogen and phosphorus removal is completed solely by biofilm and algal symbiosis system.

[0013] Further, in step S3, the desorption is performed by soaking in a 2%~5% NaOH solution for 2~4 hours. After desorption, the adsorption module is neutralized with acid to pH 7.0~8.0, then rinsed with water until neutral and returned to the reaction tank. The phosphorus-rich desorption solution is pumped into the struvite crystallization reactor, and the pH of the phosphorus-rich desorption solution is adjusted to 8.5~9.5. If the concentration of ammonium ions in the desorption solution is insufficient, ammonium chloride is added until the molar ratio of magnesium, nitrogen, and phosphorus is 1.2~1.5:1:1. The reaction is carried out for 30~60 minutes, and struvite precipitate is obtained by solid-liquid separation. The supernatant after crystallization is returned to the hydrolysis acidification tank or the immobilized biofilm reaction tank for further treatment.

[0014] Furthermore, in step S1, the particle size of the slurry produced by grinding and pulping is no greater than 2 mm; the slurry return flow rate is controlled so that the BOD5 / TN ratio in the mixed liquor entering the hydrolysis acidification tank is no less than 3 and the COD / TN ratio is no less than 6; when water quality fluctuations lead to insufficient carbon-nitrogen ratio, glucose or sodium acetate is added as a supplementary carbon source.

[0015] Furthermore, the composite filler material of the ecological stabilization pond in step S4 is obtained by mixing zeolite, biochar and oyster shells in a mass ratio of 2:2:1, and the filler material filling ratio is 20%~30%; the emergent plants are one or more combinations of reeds, cattails and calamus.

[0016] Furthermore, the disinfection method described in step S4 is ultraviolet disinfection, with an ultraviolet dose of not less than 30 mJ / cm². 2 If sodium hypochlorite is used for disinfection, the amount of chlorine added must be controlled so that the residual chlorine concentration in the effluent does not exceed 0.1 mg / L.

[0017] The present invention has the following beneficial effects: This invention grinds and slurries the residual feed and feces intercepted during the pretreatment stage of aquaculture wastewater, and then sends them to alternating hydrolysis and acidification tanks to convert them into volatile fatty acids as an endogenous carbon source. At the same time, alternating immobilized biofilm reactors are used to complete the entire process of nitrogen and phosphorus removal simultaneously within the same reaction unit. This effectively solves the problems of existing staged processes that require separate nitrogen and phosphorus removal units, resulting in large land area requirements and high operating costs due to heavy reliance on external carbon sources.

[0018] This invention sets up a detachable adsorption phosphorus removal module in an immobilized biofilm reaction tank. After adsorption saturation, the module is transferred to a regeneration unit for desorption to obtain a phosphorus-rich desorption solution. The solution is then subjected to a struvite crystallization reaction to achieve targeted recovery of phosphorus resources. The desorbed phosphorus removal module can be recycled, effectively solving the secondary pollution problems of existing chemical phosphorus removal processes that generate a large amount of phosphorus-containing hazardous waste and cannot recycle phosphorus resources.

[0019] This invention employs a dissolved oxygen feedback-controlled micro-aeration mode to match the metabolic needs of aerobic heterotrophic nitrifying-denitrifying bacteria and the algal symbiotic system. Simultaneously, it incorporates an optional micro-current enhancement system adaptable to different water quality conditions, effectively addressing the problems of existing algal treatment processes being highly susceptible to environmental factors and exhibiting insufficient stability in effluent nitrogen and phosphorus compliance during water quality fluctuations. This technical solution utilizes a modular design, eliminating the need for large-scale civil engineering modifications to existing aquaculture wastewater treatment facilities. It is widely applicable to the wastewater treatment needs of freshwater aquaculture scenarios with different species and scales, offering convenient operation and control, strong load adaptability, and significant industry promotion value. Attached Figure Description

[0020] Figure 1 This is a flowchart of a purification treatment method for achieving compliant discharge of aquaculture wastewater using microbial technology, as proposed in this invention. Figure 2 This is a bar chart comparing the removal rates of core pollutants in each experimental group proposed in this invention. Figure 3 This is a biaxial combination graph showing the operating cost and phosphorus recovery rate of each experimental group proposed in this invention; Figure 4 This is a radar chart comparing the comprehensive performance under multiple operating conditions proposed in this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] I. Explanation of Core Technical Features 1. Preparation of adsorption phosphorus removal module Modified lanthanum-based biochar was prepared by pyrolyzing corn stalks at 500℃ in the absence of air for 2 hours to obtain raw biochar. This raw biochar was then mixed with a 0.2 mol / L lanthanum chloride solution at a solid-liquid ratio of 1:10 and soaked for 12 hours. After drying, it was calcined at 400℃ for 1 hour to obtain the final product, with a lanthanum loading of approximately 35 mg / g. The modified lanthanum-based biochar was then filled into permeable PP mesh boxes (2 mm mesh size, 5 cm box thickness, 80% biochar filling rate). The module dimensions were customized according to the specifications of the reaction tank.

[0023] The module replacement cycle is dynamically adjusted based on the influent total phosphorus load. The theoretical replacement cycle is calculated using the following formula, with the effluent total phosphorus concentration reaching 1.0 mg / L as the breakthrough point: In the formula, T is the theoretical number of replacement days; M is the total mass of biochar in the module (g); q is the saturated adsorption capacity of biochar for phosphate (mg P / g, measured to be 20~25mg P / g); and Q is the daily water treatment capacity (L / d). The total phosphorus concentration in the influent is (mg / L). The replacement cycles for Examples 1-3 are 3 months, 6 months, and 4 months, respectively, which are consistent with the calculated values.

[0024] 2. Immobilization on biomembrane carriers The biofilm carrier was selected from porous polyurethane sponge (pore size 2-5 mm) or composite fiber balls. Before use, it was soaked in 1 mol / L NaOH for 24 h, rinsed with water until neutral, and then soaked in 0.5% polyethyleneimine solution for 12 h to complete surface modification, thereby increasing the positive charge density on the carrier surface and promoting microbial attachment. After inoculation with aerobic heterotrophic nitrifying-denitrifying bacteria, the biofilm was formed at 30℃ for 7 days, with a bacterial load of not less than 1.0 × 10⁻⁶. 8 CFU / g vector. Complete biofilm formation is determined by the uniform coverage of the bacterial film on the carrier surface and the absence of large areas of exposed carrier surface under microscopic examination.

[0025] The aerobic heterotrophic nitrifying-denitrifying bacterial community was composed of *Pseudomonas putida* (CGMCC 1.1821), *Bacillus subtilis* (CGMCC 1.1086), and *Alcaligenes faecalis* (CGMCC 1.1831) in a mass ratio of 2–3:1–2:1. All strains were purchased from the China General Microbiological Culture Collection Center and are commercially available.

[0026] 3. Microcurrent System Configuration The device employs parallel carbon felt anodes and cathodes arranged vertically, with an electrode spacing of 1–5 cm, and is powered by a 12V DC pulse power supply with a current density controlled at 0.1–1.0 mA / cm². 2 The operating mode is 1 hour on and 3 hours off (duty cycle 25%).

[0027] The method for verifying the uniformity of the electric field is as follows: Five measuring points are uniformly set in the horizontal direction and three measuring points are set in the vertical direction (from the water surface to the bottom of the tank) in the reaction tank, for a total of 15 measuring points. The electric field strength is measured point by point using a portable electric field strength meter, and the deviation between the electric field strength at each measuring point and the average value is calculated. If the deviation does not exceed 10%, the electric field distribution is considered uniform and qualified.

[0028] The operation and maintenance method involves wiping off any deposits on the electrode surface monthly and checking the electrode wear every six months. Electrodes should be replaced when wear exceeds 30% of their initial thickness. When the chloride ion concentration in the water exceeds 250 mg / L, to prevent the generation of free chlorine and hypochlorite ions during anodic oxidation, which could lead to electrode corrosion and byproduct formation, the microcurrent system is automatically shut down. In this case, the denitrification and phosphorus removal effect is maintained by relying on the biofilm and algal symbiotic system.

[0029] 4. Regulation of algal-bacterial symbiotic systems Chlorella (FACHB-8) was immobilized using an encapsulation method: a 2% sodium alginate solution was mixed with Chlorella lysate at a 1:1 volume ratio, and then dripped into a 1% calcium chloride solution. After solidification for 30 minutes, calcium alginate gel microspheres with a diameter of 1-2 mm were formed, with an algal cell density of 102 within each microsphere. 6 ~10 7 cells / mL, microspheres are attached to the surface of a biofilm carrier.

[0030] The illumination conditions consist of a built-in LED light source with an intensity of 2000–5000 lux and a photoperiod of 12 hours on / 12 hours in darkness. Dissolved oxygen (DO) is controlled via online feedback through the microporous aeration valve, maintaining a concentration of 0.5–2.0 mg / L. Chlorella solution is added every 15 days to maintain a stable algal concentration. Regular microscopic examination of algal cell activity within the microspheres and the algal film coverage on the carrier surface is used to maintain a biomass ratio of 3–5:1 between the inoculum and Chlorella.

[0031] 5. Discharge and disposal of excess sludge Every 7 days, the remaining sludge from the detached biofilm in the hydrolysis acidification tank and the immobilized biofilm reaction tank is discharged from the bottom sludge discharge port. After mechanical dewatering in the sludge thickening tank, it is mixed with emergent plant residues harvested from the ecological stabilization tank at a mass ratio of 2:1 and aerobic composted for 30 days. After decomposition, it is reused as base fertilizer for aquaculture ponds.

[0032] 6. Low Temperature Response Measures When the water temperature is below 15℃ in winter, the hydrolysis acidification tank and the immobilized biofilm reactor are covered with insulating blankets, and titanium alloy heating rods are installed at the bottom of the tanks to maintain the water temperature at no less than 15℃. The heating energy consumption is included in the operating cost. Simultaneously, a low-temperature resistant targeted acid-producing bacteria agent is added. This agent consists of a low-temperature resistant acid-producing bacteria group, including Clostridium butyricum and Lactococcus lactis, both of which are low-temperature adapted strains of the core functional strains in the targeted acid-producing bacteria agent. They can maintain acid-producing activity at 5~15℃, and the dosage is 100mg / L. This agent has the same function as the targeted acid-producing bacteria agent added at normal temperatures, both used to accelerate the targeted acid-producing conversion of organic matter in the hydrolysis acidification tank. The difference lies only in the adaptation and acclimatization of low-temperature resistance, representing a preferred implementation scheme for targeted acid-producing bacteria agents under low-temperature conditions.

[0033] 7. Regulating the reflux of struvite crystallization supernatant The original pH of the crystallization supernatant is 8.5-9.5. Direct reflux will disrupt the acid-producing environment of the hydrolysis acidification tank, which has a pH of 6.0-7.5. Before reflux, add 1 mol / L hydrochloric acid to adjust the pH to 6.0-7.0. The reflux ratio should be controlled at 10%-15% of the influent to avoid alkaline shocks that inhibit the activity of acid-producing bacteria.

[0034] II. Water Quality Testing Methods In the examples and comparative examples, the detection of various water quality indicators all adopted the national standard methods, as detailed below: COD: dichromate method (HJ 828-2017); Ammonia nitrogen: Nessler's reagent spectrophotometric method (HJ 535-2009); Total nitrogen (TN): alkaline potassium persulfate digestion ultraviolet spectrophotometric method (HJ 636-2012) Total phosphorus (TP): Ammonium molybdate spectrophotometric method (GB / T 11893-1989); pH: Glass electrode method (HJ 1147-2020); The effluent compliance standard is based on the first-class standard of SC / T 9101-2007 "Requirements for Freshwater Aquaculture Wastewater Discharge", with the main limits being: COD≤30mg / L, ammonia nitrogen (NH3-N, calculated as N)≤2.0mg / L (non-winter) / 3.0mg / L (winter), TN≤5.0mg / L, and TP≤0.5mg / L.

[0035] Example 1: This example treats wastewater from freshwater fishpond aquaculture, with a treatment scale of 100m³. 3 / d. Influent water quality: COD 150mg / L, NH3-N 12mg / L, TN 25mg / L, TP 3mg / L, water temperature 25℃, chloride ion concentration 120mg / L.

[0036] The specific steps are as follows: S1. Pretreatment and Preparation of Endogenous Carbon Source: The effluent is screened to remove suspended solids larger than 5mm. Retained feed and feces are ground to a particle size no larger than 2mm and slurry. This slurry, along with the screened effluent, is sent to two parallel hydrolysis acidification tanks, which operate alternately in a 12-hour cycle. A targeted acid-producing bacteria agent is added to the tanks; this agent is a mixture of Clostridium butyricum, Lactococcus lactis, and Bacillus coagulans in a 2:1:1 mass ratio. The pH of the hydrolysis acidification tanks is controlled at 6.0, with a hydraulic retention time of 6 hours. A gas collection hood with a water seal is installed at the top of the tanks to maintain an anaerobic environment, and biogas is periodically released. The slurry return flow is controlled to maintain a mixed liquor BOD5 / TN ratio of 3.2 and a COD / TN ratio of 6.5, eliminating the need for external carbon source supplementation.

[0037] S2. Simultaneous Nitrogen and Phosphorus Removal: The effluent from the hydrolysis acidification tank is fed into two sets of parallel immobilized biofilm reactors, which alternately operate on a 24-hour cycle. The reactors are filled with porous polyurethane sponge biofilm carriers at a filling ratio of 15%, and the aerobic heterotrophic nitrifying-denitrifying bacterial load is 1.2 × 10⁻⁶. 8 CFU / g carrier. Chlorella is simultaneously immobilized on the carrier surface to form a symbiotic system with a bacteria-to-algae biomass ratio of 3:1. The reaction tank is equipped with a built-in LED light source with a light intensity of 2000 lux and a photoperiod of 12 hours on / 12 hours off. The tank is filled with a removable phosphorus adsorption module at a filling ratio of 10%, with a module replacement cycle of 3 months. Microporous aeration discs are used for micro-aeration, and dissolved oxygen (DO) is maintained at 0.5 mg / L in the tank through online feedback control, with a hydraulic retention time of 8 hours. A microcurrent enhancement system is installed in the tank, with an electrode spacing of 3 cm and a current density of 0.1 mA / cm². 2 After measuring the field strength at 15 points, the field strength deviation was 7.8%, which meets the uniformity requirements.

[0038] S3. Phosphorus Removal Module Regeneration and Phosphorus Recovery: After the adsorption phosphorus removal module becomes saturated, it is removed and transferred to the regeneration unit where it is soaked in a 2% NaOH solution for 2 hours for desorption, yielding a phosphorus-rich desorbent. After desorption, the module is neutralized to pH 7.0 with 1 mol / L hydrochloric acid, rinsed with water until neutral, and returned to the reaction tank. The phosphorus-rich desorbent is sent to the struvite crystallization reactor, where the pH is adjusted to 8.5, and magnesium chloride is added to achieve a magnesium-nitrogen-phosphorus molar ratio of 1.2:1:1. The reaction is carried out for 30 minutes, and solid-liquid separation yields struvite precipitate. The supernatant from the crystallization is adjusted to pH 6.0 with 1 mol / L hydrochloric acid and refluxed to the hydrolysis acidification tank at a rate of 10% of the influent flow.

[0039] S4. Ecological Stabilization and Effluent: The effluent from the immobilized biofilm reactor is sent to the ecological stabilization tank, which is filled with a composite filler material consisting of zeolite, biochar, and oyster shells in a 2:2:1 mass ratio, at a filling ratio of 20%, and planted with emergent reeds. The effluent is then disinfected with ultraviolet light (dose 30 mJ / cm³). 2 After reaching the emission standards, emissions will be met.

[0040] Effluent water quality and compliance status: After 30 days of continuous operation and monitoring, the average COD value of the effluent was 12 mg / L, NH3-N was 1.1 mg / L, TN was 2.8 mg / L, and TP was 0.12 mg / L. All indicators met the Class I standard of SC / T 9101-2007. The COD removal rate was 92%, the TN removal rate was 89%, the TP removal rate was 96%, the phosphorus recovery rate was 82%, and the effluent compliance rate was 100%.

[0041] Example 2: This example treats the wastewater from freshwater fishponds used in winter aquaculture, with a treatment capacity of 100m³. 3 / d. Influent water quality: COD 140mg / L, NH3-N 10mg / L, TN 22mg / L, TP 2.8mg / L, initial water temperature 14℃, chloride ion concentration 110mg / L.

[0042] The specific steps are as follows: S1. Pretreatment and Preparation of Endogenous Carbon Source: The effluent is screened to remove suspended solids larger than 5mm. Retained feed and feces are ground to a particle size no larger than 2mm and slurry. This slurry, along with the screened effluent, is sent to two parallel hydrolysis acidification tanks, which operate alternately on a 24-hour cycle. A targeted acid-producing bacteria agent is added to the tanks; this agent is a mixture of Clostridium butyricum, Lactococcus lactis, and Bacillus coagulans in a 3:2:1 mass ratio. The pH of the hydrolysis acidification tanks is controlled at 7.5, with a hydraulic retention time of 12 hours. A gas collection hood with a water seal is installed at the top of the tanks to maintain an anaerobic environment, and biogas is periodically released. The slurry return flow is controlled to maintain a mixed liquor BOD5 / TN ratio of 3.5 and a COD / TN ratio of 7.0, eliminating the need for external carbon source supplementation. During winter operation, the tanks are covered with insulating blankets, and titanium alloy heating rods are installed at the bottom to maintain a water temperature no lower than 15℃. Simultaneously, 100mg / L of a low-temperature resistant targeted acid-producing bacteria agent is added.

[0043] S2. Simultaneous Nitrogen and Phosphorus Removal: The effluent from the hydrolysis acidification tank is fed into two sets of parallel immobilized biofilm reactors, which alternately operate on a 24-hour cycle. The reactors are filled with a combined fiber ball biofilm carrier at a filling ratio of 30%, and the aerobic heterotrophic nitrifying-denitrifying bacterial load is 1.5 × 10⁻⁶. 8CFU / g carrier. Chlorella is simultaneously immobilized on the carrier surface to form a symbiotic system with a bacteria-to-algae biomass ratio of 5:1. The reaction tank is equipped with a built-in LED light source with a light intensity of 5000 lux and a photoperiod of 12 hours on / 12 hours off. The tank is filled with removable phosphorus adsorption modules at a filling ratio of 20%, with a module replacement cycle of 6 months. Micro-aeration is achieved using microporous aeration discs, and dissolved oxygen (DO) is maintained at 2.0 mg / L through online feedback control, with a hydraulic retention time of 16 hours. A microcurrent enhancement system is installed in the tank, with an electrode spacing of 5 cm and a current density of 1.0 mA / cm². 2 After measuring the field strength at 15 points, the field strength deviation was 8.7%, which meets the uniformity requirements.

[0044] S3. Phosphorus Removal Module Regeneration and Phosphorus Recovery: After the adsorption phosphorus removal module becomes saturated, it is removed and transferred to the regeneration unit where it is soaked in a 5% NaOH solution for 4 hours to desorb, obtaining a phosphorus-rich desorbent. After desorption, the module is neutralized to pH 8.0 with 1 mol / L hydrochloric acid, rinsed with water until neutral, and returned to the reaction tank. The phosphorus-rich desorbent is sent to the struvite crystallization reactor, where the pH is adjusted to 9.5, and magnesium chloride is added to make the magnesium-nitrogen-phosphorus molar ratio 1.5:1:1. The reaction is carried out for 60 minutes, and the struvite precipitate is obtained through solid-liquid separation. The supernatant from the crystallization is adjusted to pH 7.0 with 1 mol / L hydrochloric acid and refluxed to the hydrolysis acidification tank at a ratio of 15% of the influent.

[0045] S4. Ecological Stabilization and Effluent: The effluent from the immobilized biofilm reactor is sent to the ecological stabilization tank, which is filled with a composite packing material consisting of zeolite, biochar, and oyster shells in a 2:2:1 mass ratio, at a filling ratio of 30%, and planted with emergent plants such as cattails. The effluent is disinfected with ultraviolet light (dose 50 mJ / cm³). 2 After reaching the emission standards, emissions will be met.

[0046] Effluent water quality and compliance status: After 30 days of continuous operation and monitoring, the average COD of the effluent was 17 mg / L, NH3-N was 1.5 mg / L, TN was 3.3 mg / L, and TP was 0.20 mg / L. All indicators met the Class I standard of SC / T 9101-2007 (TN ≤ 5.0 mg / L in winter, and NH3-N is limited to 3.0 mg / L in winter). The COD removal rate was 88%, the TN removal rate was 85%, the TP removal rate was 93%, the phosphorus recovery rate was 79%, and the effluent compliance rate was 100%. The relative operating cost was 0.61, including the electricity consumption for winter insulation and heating.

[0047] Example 3: This example treats wastewater from high-density freshwater aquaculture, with a treatment scale of 100m³. 3 / d. Influent water quality: COD 240mg / L, NH3-N 18mg / L, TN 40mg / L, TP 5mg / L, water temperature 28℃, chloride ion concentration 200mg / L.

[0048] The specific steps are as follows: S1. Pretreatment and Endogenous Carbon Source Preparation: The effluent is screened to remove suspended solids larger than 5mm. Retained feed and feces are ground to a particle size no larger than 2mm and slurry. This slurry, along with the screened effluent, is sent to two parallel hydrolysis acidification tanks, which operate alternately in 18-hour cycles. Targeted acid-producing bacteria are added to the tanks; the bacteria are a mixture of Clostridium butyricum, Lactococcus lactis, and Bacillus coagulans in a mass ratio of 2.5:1.5:1. The pH of the hydrolysis acidification tanks is controlled at 6.8, with a hydraulic retention time of 9 hours. A gas collection hood with a water seal is installed at the top of the tanks to maintain an anaerobic environment, and biogas is periodically released. The slurry return flow is controlled to maintain a mixed liquor BOD5 / TN ratio of 3.3 and a COD / TN ratio of 6.8, eliminating the need for external carbon source supplementation.

[0049] S2. Simultaneous Nitrogen and Phosphorus Removal: The effluent from the hydrolysis acidification tank is fed into two sets of parallel immobilized biofilm reactors, which alternately operate on a 24-hour cycle. The reactors are filled with porous polyurethane sponge biofilm carriers at a filling ratio of 22%, and the aerobic heterotrophic nitrifying-denitrifying bacterial load is 1.3 × 10⁻⁶. 8 CFU / g carrier. Chlorella is simultaneously immobilized on the carrier surface to form a symbiotic system with a bacteria-to-algae biomass ratio of 4:1. The reaction tank is equipped with a built-in LED light source with a light intensity of 3500 lux and a photoperiod of 12 hours on / 12 hours off. The tank is filled with a removable phosphorus adsorption module at a filling ratio of 15%, with a module replacement cycle of 4 months. Microporous aeration discs are used for micro-aeration, and dissolved oxygen (DO) is maintained at 1.2 mg / L in the tank through online feedback control, with a hydraulic retention time of 12 hours. A microcurrent enhancement system is installed in the tank, with an electrode spacing of 4 cm and a current density of 0.5 mA / cm². 2 After measuring the field strength at 15 points, the field strength deviation was 7.2%, which meets the uniformity requirements.

[0050] S3. Phosphorus Removal Module Regeneration and Phosphorus Recovery: After the adsorption phosphorus removal module becomes saturated, it is removed and transferred to the regeneration unit where it is soaked in a 3.5% NaOH solution for 3 hours for desorption, yielding a phosphorus-rich desorbent. After desorption, the module is neutralized to pH 7.5 with 1 mol / L hydrochloric acid, rinsed with water until neutral, and returned to the reaction tank. The phosphorus-rich desorbent is sent to the struvite crystallization reactor, where the pH is adjusted to 9.0, and magnesium chloride is added to achieve a magnesium-nitrogen-phosphorus molar ratio of 1.35:1:1. The reaction is carried out for 45 minutes, and solid-liquid separation yields struvite precipitate. The supernatant from the crystallization is adjusted to pH 6.5 with 1 mol / L hydrochloric acid and refluxed to the hydrolysis acidification tank at a ratio of 12% of the influent flow.

[0051] S4. Ecological Stabilization and Effluent: The effluent from the immobilized biofilm reactor is sent to the ecological stabilization tank, which is filled with a composite packing material consisting of zeolite, biochar, and oyster shells in a 2:2:1 mass ratio, with a filling ratio of 25%, and planted with emergent plants such as calamus. The effluent is disinfected with ultraviolet light (dose 40 mJ / cm³). 2 After reaching the emission standards, emissions will be met.

[0052] Effluent water quality and compliance status: After 30 days of continuous operation and monitoring, the average COD of the effluent was 24 mg / L, NH3-N was 1.8 mg / L, TN was 4.0 mg / L, and TP was 0.25 mg / L. All indicators met the Class I standard of SC / T 9101-2007. The COD removal rate was 90%, the TN removal rate was 90%, the TP removal rate was 95%, the phosphorus recovery rate was 85%, and the effluent compliance rate was 100%.

[0053] Example 4: This example treats freshwater aquaculture wastewater from coastal areas. Due to seawater intrusion, the treatment scale is 100m³. 3 / d. Influent water quality: COD 150mg / L, TN 25mg / L, TP 3mg / L, water temperature 25℃, chloride ion concentration 300mg / L. The process is exactly the same as in Example 1, except that: when the microcurrent system in the immobilized biofilm reactor is running, the online chloride ion electrode monitors the chloride ion concentration to be 300mg / L, and the microcurrent system is automatically shut down, with the biofilm algae-bacterial symbiotic system solely responsible for the water purification function. The remaining units operate normally.

[0054] Operational Results: After 30 days of continuous monitoring, the average effluent COD was 15 mg / L, TN was 3.0 mg / L, and TP was 0.15 mg / L, with COD removal rates of 90%, TN removal rates of 88%, and TP removal rates of 95%, all meeting the Class I standard of SC / T 9101-2007. Compared with Example 1, the TN removal rate decreased by 1 percentage point, but the effluent still consistently met the standards. Simultaneously, the corrosion rate of the carbon felt electrode decreased from 0.5% / month under normal operating conditions to 0.1% / month after shutdown, extending the electrode's lifespan. This indicates that shutting down the microcurrent system when the chloride ion concentration exceeds 250 mg / L will not cause the effluent to exceed the standard and is beneficial for equipment protection.

[0055] IV. Comparative Examples The influent water quality of all comparative examples was completely consistent with that of Example 1, and the treatment capacity of all examples was 100m³. 3 / d. The scale settings are as follows: Comparative Example 1: Using traditional A 2 The / O segmented nitrogen and phosphorus removal process has an anaerobic tank HRT of 2h, an anoxic tank HRT of 3h, and an aerobic tank HRT of 5h (total HRT 10h). The nitrification liquor return ratio is 200%, the sludge return ratio is 100%, and sodium acetate is added as an exogenous carbon source. The addition amount is calculated based on BOD5 / TN=4:1. Polyaluminum chloride (addition amount 30mg / L) is added at the end of the aerobic tank for chemical phosphorus removal. The effluent from the secondary sedimentation tank is discharged after passing through an ecological stabilization tank and ultraviolet disinfection.

[0056] Comparative Example 2: The process is exactly the same as in Example 1, except that no targeted acid-producing bacteria agent is added to the hydrolysis acidification tank, and hydrolysis acidification is carried out by relying on the natural bacterial community in the water.

[0057] Comparative Example 3: The process is exactly the same as in Example 1, except that the immobilized biofilm reactor is not equipped with an adsorption phosphorus removal module, and instead polyaluminum chloride is added in the aerobic section: the dosage is 30 mg / L for chemical phosphorus removal.

[0058] Comparative Example 4: The process was exactly the same as in Example 1, except that the microcurrent enhancement system was turned off.

[0059] Comparative Example 5: The process is basically the same as that of Example 1, but the immobilized biofilm reactor is only set up as a single group (not two groups operating in parallel alternately). After the adsorption and phosphorus removal module is saturated, it needs to be shut down for 2 hours for replacement and regeneration. During the replacement period, the tank stops processing.

[0060] Comparative Example 6: The process was exactly the same as in Example 1, but Chlorella was not immobilized, no artificial light source was used, and the biofilm carrier was only attached to aerobic heterotrophic nitrifying-denitrifying bacteria.

[0061] V. Experimental Results and Analysis Table 1 Comparison of core operating parameters for each experimental group

[0062] This table clarifies the differences in core parameters among the experimental groups. Examples 1 to 4 all adopt the full process technical route of the present invention. Comparative Example 1 is a prior art solution, and Comparative Examples 2 to 6 correspond to working conditions lacking specific core features. The remaining variables are controlled to be completely consistent with Example 1, and the comparison results are valid.

[0063] Table 2 Comparison of influent and effluent water quality and treatment effect in each experimental group

[0064] Note 1: Relative operating costs are expressed as a comparative example 1 (A 2 The operating cost per ton of water for the (external carbon source + chemical phosphorus removal) method is based on a benchmark of 1.00. The calculation includes electricity costs, chemical costs such as carbon source, phosphorus removal agent, desorbent, pH adjuster, etc., sludge treatment costs, and labor costs, but excludes equipment depreciation. All examples and comparative examples are based on the same treatment capacity of 100m³. 3 / d and operating condition calculations.

[0065] Note 2: Effluent compliance rate = Number of days meeting standards / Total number of operating days × 100%, calculated based on 30 days of continuous operation. The judgment criteria are SC / T 9101-2007 Class I standards (COD≤30mg / L, NH3-N≤2.0mg / L, TN≤5.0mg / L, TP≤0.5mg / L). In Example 2, according to the winter standard, the effluent NH3-N was 1.5mg / L, which is lower than the 2.0mg / L limit, thus meeting the standard.

[0066] Note 3: The operating cost of Example 2 includes the electricity consumption for winter insulation and heating.

[0067] This table presents the actual treatment effects of each experimental group. Examples 1-4 show higher nitrogen and phosphorus removal rates and effluent compliance rates than their respective control groups, with operating costs only slightly higher than traditional A. 2 The / O process achieves a phosphorus recovery rate of 50%~61%, with a stable phosphorus recovery rate of over 79%. This verifies that the core technical features of this invention address the shortcomings of existing technologies, such as high carbon source cost, difficulty in phosphorus recovery, poor stability in meeting standards, and large footprint. The process adaptability covers various aquaculture wastewater conditions, including conventional, low temperature, high load, and high chloride ion conditions.

[0068] refer to Figure 2 This figure visually compares the pollutant removal capabilities of the complete process of this invention, existing mainstream processes, and processes lacking core technology units. It is evident that the removal rates of all three types of pollutants in Example 1 are the highest among all groups. Comparative Example 2, due to the lack of targeted acid-producing bacteria, suffers from insufficient endogenous carbon source supply, resulting in a TN removal rate of only 65%, far lower than the complete process. This verifies that the targeted acid-producing bacteria agent is the core for ensuring denitrification efficiency. Comparative Example 4, lacking microcurrent enhancement, shows a 13 percentage point decrease in TN removal rate, demonstrating the enhancing effect of microcurrent on microbial denitrification activity. Comparative Example 1, with its traditional process, achieves a TN removal rate of only 78%, requiring high-cost external carbon source supplementation to barely improve denitrification efficiency. This figure directly verifies the synergistic effect of the core technology units of this process, effectively addressing the shortcomings of low denitrification efficiency and unstable operation in existing technologies.

[0069] refer to Figure 3 This figure visually demonstrates the dual advantages of this process in terms of economy and resource recovery. Example 1 has a relative operating cost of only 0.52, a 48% reduction compared to traditional processes, while achieving a phosphorus recovery rate of 82%, realizing synergistic benefits of cost reduction and resource recovery. Comparative Example 3, lacking an adsorption phosphorus removal module, employs a chemical phosphorus removal process, resulting in an operating cost of 0.76 and a phosphorus recovery rate of 0%, failing to achieve phosphorus resource recycling and generating phosphorus-containing hazardous waste, increasing secondary treatment costs. Comparative Example 2 nominally has an operating cost close to that of Example 1, but due to insufficient denitrification efficiency, additional carbon source is required to meet standards, making the actual overall operating cost higher than this process. This figure verifies the core advantages of this process: adsorption-crystallization phosphorus recovery and efficient utilization of endogenous carbon sources, addressing the shortcomings of existing technologies such as high operating costs and phosphorus resource waste.

[0070] refer to Figure 4 This radar chart comprehensively compares the performance of this invention with that of traditional processes under four typical freshwater aquaculture effluent conditions from three dimensions: treatment effect, economy, and resource recovery. It is evident that the closed polygon areas corresponding to Examples 1-4 are all significantly larger than those corresponding to Comparative Example 1, indicating that this invention can maintain excellent pollutant removal efficiency, low operating costs, and stable phosphorus recovery rates under four conditions: conventional, low temperature, high load, and high chloride ion. Specifically, under high chloride ion conditions, stable compliance can still be achieved even after the microcurrent is shut off. Under low temperature conditions, a TN removal rate of over 85% can still be maintained through insulation and the addition of low-temperature resistant bacterial agents, without requiring significant additional operating costs. This chart verifies the wide adaptability of this process, overcoming the shortcomings of existing technologies, such as narrow operating condition adaptability and low effluent compliance rates under low temperature and high load conditions.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for purifying aquaculture wastewater to meet discharge standards using microbial technology, characterized in that, Includes the following steps: S1. Pretreatment and preparation of endogenous carbon source: After the aquaculture tailwater is treated by a screen to remove large particulate suspended matter, the retained feed and feces are ground into slurry and sent together with the screen effluent into at least two sets of closed hydrolysis acidification tanks that are connected in parallel and operate alternately. Targeted acid-producing bacteria are added to the tanks to convert macromolecular organic matter into volatile fatty acids as endogenous carbon sources for subsequent treatment. S2, Simultaneous nitrogen and phosphorus removal: The effluent from the hydrolysis acidification tank is sent to at least two sets of parallel, alternating immobilized biofilm reaction tanks. The reaction tanks are filled with biofilm carriers and detachable adsorption phosphorus removal modules. The biofilm carriers are immobilized with aerobic heterotrophic nitrification-denitrification bacteria. Under micro-aeration conditions, the endogenous carbon source obtained in S1 is used to simultaneously complete organic matter degradation, ammonia nitrogen oxidation and denitrification in the same tank. At the same time, phosphate is enriched by the adsorption phosphorus removal module. S3. Phosphorus Removal Module Regeneration and Phosphorus Recovery: After the phosphorus removal module is saturated, it is taken out from the operating reaction tank and transferred to the regeneration unit for desorption to obtain phosphorus-rich desorption solution. At the same time, another set of reaction tanks is switched to operation. The phosphorus-rich desorption solution recovers phosphorus through struvite crystallization reaction. The desorbed adsorption module is returned to the reaction tank for reuse after neutralization and cleaning. S4. Ecological Stabilization and Effluent: The effluent from the immobilized biofilm reactor is sent to the ecological stabilization tank. The residual nitrogen and phosphorus are removed by the adsorption and interception of composite packing and the absorption of emergent plants. The nitrogen and phosphorus are removed from the system through plant harvesting and packing regeneration. The effluent is then disinfected and discharged or reused.

2. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, In step S1, the two sets of hydrolysis acidification tanks are operated alternately in a 12-24 hour cycle. The directional acid-producing bacteria agent is a composition of Clostridium butyricum, Lactococcus lactis and Bacillus coagulans in a mass ratio of 2-3:1-2:

1. The pH of the hydrolysis acidification tank is controlled at 6.0-7.5, and the hydraulic retention time is 6-12 hours. The top of the sealed tank of the hydrolysis acidification tank is equipped with a gas collection hood and a water seal device.

3. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, In step S2, the biofilm carrier is a porous polyurethane sponge or a combination of fiber balls, and the adsorption phosphorus removal module is a permeable grid box with built-in modified lanthanum-based biochar. The modified lanthanum-based biochar is filled in the grid box. The filling ratio of the biofilm carrier in the reaction tank is 15%~30%, and the filling ratio of the adsorption phosphorus removal module is 10%~20%.

4. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, The aerobic heterotrophic nitrifying-denitrifying bacterial community mentioned in step S2 is a compound bacterial agent of Pseudomonas, Bacillus, and Alcaligenes; Chlorella is also immobilized on the surface of the biofilm carrier to form a bacterial-algal symbiotic system, and the biomass ratio of bacterial agent to Chlorella is 3~5:1; the immobilized biofilm reaction tank is equipped with a light-transmitting window or a built-in LED light source with a light intensity of 2000~5000 lux.

5. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, The micro-aeration described in step S2 uses microporous aeration discs, and the aeration rate is controlled by dissolved oxygen feedback to maintain the dissolved oxygen concentration in the reaction tank at 0.5~2.0 mg / L, the reaction temperature at 15~35℃, and the hydraulic retention time at 8~16h.

6. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, The reaction cell described in step S2 is further equipped with a microcurrent enhancement system, which includes electrodes and a power source. The electrodes are carbon felt electrodes with an electrode spacing of 1-5 cm and a current density of 0.1-1.0 mA / cm². 2 It uses DC or pulse power supply, and is powered on for 1 hour and then off for 3 hours. The microcurrent enhancement system is suitable for freshwater aquaculture wastewater with chloride ion concentration below 250 mg / L. When the chloride ion concentration is higher than 250 mg / L, the microcurrent system stops operating and nitrogen and phosphorus removal is completed solely by biofilm and algal symbiosis system.

7. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, In step S3, the desorption is performed by soaking in a 2% to 5% NaOH solution for 2 to 4 hours. After the desorption is completed, the adsorption module is neutralized with acid to pH 7.0 to 8.0, then rinsed with water until neutral and returned to the reaction tank. The phosphorus-rich desorption solution is pumped into the struvite crystallization reactor, and the pH of the phosphorus-rich desorption solution is adjusted to 8.5~9.

5. If the concentration of ammonium ions in the desorption solution is insufficient, ammonium chloride is added until the molar ratio of magnesium, nitrogen and phosphorus is 1.2~1.5:1:

1. The reaction is carried out for 30~60 minutes, and struvite precipitate is obtained by solid-liquid separation. The supernatant after crystallization is returned to the hydrolysis acidification tank or the immobilized biofilm reaction tank for further treatment.

8. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, In step S1, the particle size of the slurry produced by grinding and pulping is no greater than 2 mm; the slurry return flow rate is controlled so that the BOD5 / TN ratio in the mixed liquor entering the hydrolysis acidification tank is no less than 3 and the COD / TN ratio is no less than 6; when water quality fluctuations lead to insufficient carbon-nitrogen ratio, glucose or sodium acetate is added as a supplementary carbon source.

9. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, The composite filler in the ecological stabilization pond in step S4 is obtained by mixing zeolite, biochar and oyster shells in a mass ratio of 2:2:1, and the filler ratio is 20%~30%; the emergent plants are one or more combinations of reeds, cattails and calamus.

10. The purification treatment method for achieving standard discharge of aquaculture wastewater using microbial technology according to claim 1, characterized in that, The disinfection method described in step S4 is ultraviolet disinfection, with an ultraviolet dose of not less than 30 mJ / cm². 2 If sodium hypochlorite is used for disinfection, the amount of chlorine added must be controlled so that the residual chlorine concentration in the effluent does not exceed 0.1 mg / L.

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