Bacteria-algae symbiotic integrated culture tail water treatment system and method

Abstract

The invention discloses a bacterial-algae symbiotic integrated culture tail water treatment system and method. The culture tail water treatment system comprises a regulating reservoir, a submersible sewage pump, a multi-stage coupling biochemical treatment unit and a shellfish purification unit, the submersible sewage pump is arranged at an outlet of the adjusting tank; the multi-stage coupling biochemical treatment unit comprises an aeration biochemical pool, a biological filter bed and an aerobic denitrification microalgae biological membrane unit which are sequentially connected in series; the biological filter bed takes a rice husk layer and a pelelith layer as biological carriers; the aerobic denitrification microalgae biological membrane unit comprises microalgae and functional bacteria, the functional bacteria are bacilli weldmanni and escherichia marmoreus, the microalgae fix CO2 and release oxygen through photosynthesis, and the functional bacteria degrade nitrides through heterotrophic nitrification-aerobic denitrification; the shellfish purification unit is arranged at the water outlet end of the multi-stage coupling biochemical treatment unit and is used for filtering residual microalgae and suspended particulate matters in the water body. The invention further provides a tail water treatment method, nitrogen and phosphorus are efficiently removed, energy consumption is reduced, secondary pollution is avoided, and resource utilization can be achieved.

Description

Technical Field

[0001] This invention relates to the field of aquaculture wastewater treatment technology, and more specifically, to an integrated system and method for treating aquaculture wastewater using bacteria and algae symbiosis. Background Technology

[0002] In recent years, the scale of my country's aquaculture industry has continued to expand. However, traditional extensive (pond aquaculture) and semi-extensive (cage aquaculture) models have problems such as difficulty in controlling water quality, low water resource utilization, and frequent disease outbreaks. With the increase in aquaculture density, pollution of aquaculture wastewater (excessive nitrogen and phosphorus nutrients, accumulation of organic matter, and proliferation of pathogenic microorganisms) has become increasingly serious, leading to eutrophication of water bodies and restricting the sustainable development of the industry.

[0003] To address pollution issues, existing technologies for treating aquaculture wastewater mainly include: Physical precipitation and chemical oxidation methods can reduce pollution in the short term, but they have problems such as high energy consumption, high operating costs, and easy generation of secondary pollution (such as chemical residues). They also cannot solve the problem of nitrate accumulation caused by insufficient carbon sources in water bodies with low C / N ratios (usually <5). Biofilm method and ecological pond / ecological floating bed method: rely on microorganisms or aquatic plants for purification. The treatment cost is low, but the area required is large, the treatment efficiency is low (total nitrogen removal rate is usually <60%), and the adaptability to environmental changes (such as temperature and light) is poor, making it difficult to meet the treatment needs of high-density aquaculture wastewater. Single microalgae treatment technology: Microalgae can absorb nitrogen and phosphorus and release oxygen, but when used alone, the ammonia nitrogen removal capacity is limited (removal rate <70%), the system stability is significantly affected by light and temperature, and it cannot simultaneously solve the problems of pathogen residue and biosafety in the recycling of tailwater. Existing recirculating aquaculture systems, while capable of water resource recycling, still rely on traditional technologies for their core water treatment units, resulting in drawbacks such as low nitrogen and phosphorus removal efficiency, the need for external carbon sources (such as methanol), and high operating energy consumption (aeration energy consumption accounts for more than 40% of the total system energy consumption). Summary of the Invention

[0004] In view of this, the primary objective of the present invention is to overcome the above-mentioned defects of the prior art and provide an integrated aquaculture wastewater treatment system and method for bacteria and algae symbiosis, so as to at least solve the technical problems of existing aquaculture wastewater treatment technologies that cannot efficiently remove nitrogen and phosphorus, have high energy consumption, cause secondary pollution, and cannot be utilized as resources, and are not adaptable to different geographical scenarios.

[0005] To address the aforementioned problems, the primary objective of this invention is to provide an integrated aquaculture wastewater treatment system comprising an equalization tank, a submersible pump, a multi-stage coupled biochemical treatment unit, and a shellfish purification unit. The submersible pump is located at the outlet of the equalization tank and is used to transport the effluent to the multi-stage coupled biological treatment unit. The multi-stage coupled biological treatment unit includes an aerated biological treatment tank, a biological filter bed, and an aerobic denitrifying microalgae biofilm unit connected in series. The biological filter bed uses rice husk layer and volcanic rock layer as biological carriers. The aerobic denitrifying microalgae biofilm unit contains microalgae and functional bacteria. The functional bacteria are Bacillus widmannii and Escherichia coli. The microalgae fix CO2 and release oxygen through photosynthesis, and the functional bacteria degrade nitrogen oxides through heterotrophic nitrification-aerobic denitrification. The shellfish purification unit is located at the outlet of the multi-stage coupled biological treatment unit and is used to filter residual microalgae and suspended particulate matter in the water.

[0006] Preferably, the multi-stage coupled biochemical processing unit is a 2-4 stage series module, with a single module processing capacity of 20-50m³. 3 / sky.

[0007] Preferably, the rice husk layer in the biofilter bed has a thickness of 20-40cm, the volcanic rock layer has a thickness of 40-60cm, and the rice husk layer is located above the volcanic rock layer.

[0008] Preferably, the microalgae in the aerobic denitrifying microalgae biofilm unit are at least one of Chlorella and Scenedesmus, and the initial inoculation concentration of the microalgae is 1×10⁻⁶. 6 -5×10 6 cells / mL.

[0009] Preferably, the shellfish introduced into the shellfish purification unit are freshwater shellfish selected from at least one of freshwater mussels and razor clams, with a stocking density of 5-10 shellfish / m². 3 .

[0010] Preferably, it also includes a microalgae biomass recovery unit, which is set at the sludge discharge port of the aerobic denitrifying microalgae biofilm unit and is used for centrifugation, drying and recovery of microalgae biomass.

[0011] Preferably, the aerated biological treatment tank is equipped with microporous aerators, and the aeration intensity is 0.5-1.2 m. 3 / (m 2 •h), the residence time of the effluent in the aerated biological treatment tank is ≥6h.

[0012] Preferably, the aerobic denitrifying microalgae biofilm unit further includes a temperature control device and a supplemental lighting device, wherein the temperature inside the control unit is 15-30℃ and the light intensity is 2000-5000 lux.

[0013] The second objective of this invention is to provide a method for treating wastewater from an integrated aquaculture system based on the aforementioned system, comprising the following steps: S1: Wastewater buffer, aquaculture wastewater is discharged into the equalization tank to homogenize the water quality, and the buffering time is 2-4 hours; S2: Aerobic conversion. The submersible sewage pump transports the effluent from the equalization tank to the aerated biological treatment tank. Under aeration conditions, the reaction lasts for 6-12 hours, converting ammonia nitrogen into nitrate nitrogen. S3: Biological filtration. The effluent from the aerated biological treatment tank enters the biological filter bed, where it is adsorbed by the rice husk layer and degraded by microorganisms in the volcanic rock layer to remove recalcitrant nitrogenous substances and organic matter. S4: Algal-microbe symbiotic degradation. The effluent from the biofilter enters the aerobic denitrification microalgae biofilm unit, where it is circulated and degraded for 6-10 hours at 15-30℃ and 2000-5000 lux, achieving nitrogen and phosphorus removal. S5: Shellfish purification. The effluent from the aerobic denitrification microalgae biofilm unit enters the shellfish purification unit and is treated for 4-8 hours before being discharged in compliance with standards or recycled.

[0014] Preferably, in step S4, the inoculation ratio of microalgae to functional bacteria in the aerobic denitrifying microalgae biofilm unit is (1×10⁻⁶). 6 -5×10 6 cells / mL): (1×10 8 -5×10 8 (CFU / mL).

[0015] Preferably, it also includes step S6: resource recycling; Algae-rich sludge is periodically discharged from the aerobic denitrifying microalgae biofilm unit, and the microalgae biomass is recovered through centrifugation and drying; shellfish are harvested as by-products after they mature.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This integrated aquaculture wastewater treatment system, combining bacteria and algae, includes an equalization tank, submersible pumps, multi-stage coupled biochemical treatment units, and a shellfish purification unit. The equalization tank buffers the wastewater, homogenizing its quality and quantity; its design volume matches the treatment capacity. Submersible pumps are located at the outlet of the equalization tank to transport the wastewater to the subsequent multi-stage coupled biochemical treatment units. These units employ a modular design, with each module having a treatment capacity of 20-50 m³ / h. 3 The system operates per day, and the number of modules can be increased or decreased according to the scale of aquaculture. The aerated biological treatment tank achieves aerobic reactions through aeration, converting ammonia nitrogen in the effluent into nitrate nitrogen. The effluent retention time is ≥6 hours, and the aeration intensity is 0.5-1.2 m³ / h. 3 / (m 2•h); The biofilter uses rice husk and volcanic rock layers as biological carriers, with the rice husk layer on top and the volcanic rock layer below, providing an attachment and growth environment for microorganisms while promoting denitrification and organic matter degradation; the aerobic denitrifying microalgae biofilm unit contains a symbiotic biofilm formed by microalgae and functional bacteria. The functional bacteria achieve heterotrophic nitrification-aerobic denitrification, while microalgae 331 fix CO2 and absorb NH4 through photosynthesis. + PO4 3- Simultaneously, it releases oxygen for the metabolism of functional bacteria, forming a closed metabolic loop of microalgae carbon fixation and oxygen supply, and bacterial degradation and feedback, without the need for an external carbon source; the shellfish purification unit is set at the effluent end of the multi-stage coupled biochemical treatment unit, and freshwater shellfish (such as river mussels and razor clams) are introduced at a density of 5-10 per m³. 3 The process involves shellfish filter-feeding to remove residual microalgae, suspended particulate matter, and organic / inorganic particulate matter from the water, transferring the nitrogen and phosphorus absorbed by the microalgae into the shellfish, and harvesting them as byproducts after the shellfish mature. Through a four-stage synergistic treatment process involving aeration conversion, biological filtration, algal-bacterial symbiotic degradation, and shellfish purification, the total nitrogen removal rate is >90%, and the total phosphorus removal rate is >85%, with effluent quality meeting the discharge standards for aquaculture tailwater pollutants. Relying on the closed-loop metabolism of microalgae and bacteria, no external carbon source is required, and the operating energy consumption (mainly water circulation and aeration) is reduced by 30%-40% compared to traditional RAS systems. Each ton of dry matter from microalgae can fix 1.8 tons of CO2, enhancing the potential for carbon emission reduction throughout the entire life cycle compared to traditional technologies. The entire process uses biological methods (microalgae, bacteria, and shellfish), without the addition of chemical agents, avoiding chemical residues and secondary pollution. Microalgae biomass can produce high-protein feed annually, and shellfish are harvested as a by-product, converting treatment costs into economic benefits and supporting low-carbon aquaculture certification. The modular design allows for flexible addition or removal of treatment modules, adapting to the geographical conditions of land scarcity in lake areas and decentralized aquaculture (small modules can be deployed nearby). Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the integrated aquaculture wastewater treatment system for bacteria and algae symbiosis in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structural framework of the integrated aquaculture wastewater treatment system for bacteria and algae symbiosis in an embodiment of the present invention; Figure 3 This is a schematic diagram of the process for treating wastewater from integrated aquaculture with bacteria and algae in an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached figures: 1-Equalization tank; 2-Submersible sewage pump; 3-Multi-level coupled biochemical processing unit; 31-Aerated biological treatment tank; 32-Biofilter bed; 321-Rice husk layer; 322-Volcanic rock layer; 33-Aerobic denitrifying microalgae biofilm unit; 331-Microalgae; 332-Functional bacteria; 333-Temperature control device; 334-Supplemental lighting device; 4-Shellfish purification unit; 5-Microalgae biomass recovery unit. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] The terms “upper,” “lower,” “left,” “right,” and similar expressions used in this document are for illustrative purposes only and do not represent the only possible implementation.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. Please see Figure 1-2 As shown in the figure, this embodiment of the invention provides an integrated aquaculture wastewater treatment system for bacteria and algae symbiosis. The wastewater treatment system includes an equalization tank 1, a submersible pump 2, a multi-stage coupled biochemical treatment unit 3, and a shellfish purification unit 4, wherein: Submersible pump 2 is installed at the outlet of equalization tank 1 to transport effluent to multi-stage coupled biochemical treatment unit 3. Multi-stage coupled biochemical treatment unit 3 includes an aeration biochemical tank 31, a biofilter 32, and an aerobic denitrifying microalgae biofilm unit 33 connected in series. The biofilter 32 uses rice husk layer 321 and volcanic rock layer 322 as biological carriers. The aerobic denitrifying microalgae biofilm unit 33 contains microalgae 331 and functional bacteria 332. The functional bacteria 332 are Bacillus widmannii and Escherichia coli. Microalgae 331 fixes CO2 and releases oxygen through photosynthesis. Functional bacteria 332 degrade nitrogen oxides through heterotrophic nitrification-aerobic denitrification. Shellfish purification unit 4 is installed at the outlet of multi-stage coupled biochemical treatment unit 3 to filter residual microalgae and suspended particulate matter in the water.

[0022] Specifically, in this embodiment, the equalization tank 1 is used to buffer aquaculture wastewater and equalize water quality and quantity, and its design volume matches the treatment scale; the submersible pump 2 is located at the outlet of the equalization tank 1 and is used to transport the wastewater to the subsequent multi-stage coupled biological treatment unit 3; the multi-stage coupled biological treatment unit 3 adopts a modular design, and its single-module treatment capacity is 20-50m³. 3 / day, and the number of modules can be increased or decreased according to the scale of aquaculture. Among them, the aerated biological treatment tank 31 achieves aerobic reaction through aeration, converting ammonia nitrogen in the effluent into nitrate nitrogen. The effluent retention time is ≥6h, and the aeration intensity is 0.5-1.2m 3 / (m 2 •h); The biofilter uses rice husk and volcanic rock layers as biological carriers, with the rice husk layer on top and the volcanic rock layer below, providing an attachment and growth environment for microorganisms while promoting denitrification and organic matter degradation; the aerobic denitrifying microalgae biofilm unit 33 contains a symbiotic biofilm formed by microalgae 331 and functional bacteria 332. The functional bacteria 332 achieve heterotrophic nitrification-aerobic denitrification, while the microalgae 331 fixes CO2 and absorbs NH4 through photosynthesis. + PO4 3- Simultaneously, it releases oxygen for the metabolism of functional bacteria, forming a closed metabolic loop of microalgae carbon fixation and oxygen supply, and bacterial degradation and feedback, without the need for an external carbon source; the shellfish purification unit 4 is located at the outlet of the multi-stage coupled biochemical treatment unit 3, and freshwater shellfish (such as river mussels and razor clams) are introduced at a density of 5-10 per m³. 3 The system removes residual microalgae, suspended particulate matter, and organic / inorganic particulate matter from the water by filter feeding on shellfish. The nitrogen and phosphorus absorbed by the microalgae 331 are transferred to the shellfish body, and the shellfish are harvested as a by-product after they mature.

[0023] Specifically, please refer to Figure 1 As shown, in some embodiments of the present invention, the multi-stage coupled biochemical processing unit 3 is a 2-4 stage series module, with a single module processing capacity of 20-50m³. 3 / sky.

[0024] Considering that the single module of the multi-level coupled biochemical treatment unit 3 is essentially a functional combination of an aerated biochemical tank, a biofilter, and an aerobic denitrifying microalgae biofilm unit, its core purification principle relies on the closed-loop metabolism of microalgae and bacteria. Microalgae 331 fix CO2 and absorb NH4 through photosynthesis. + PO4 3- At the same time, it releases oxygen; functional bacteria 332 (Bacillus wedemannii, Escherichia coli) degrade nitrogen compounds through heterotrophic nitrification-aerobic denitrification, producing CO2 to feed back to microalgae, without the need for an external carbon source.

[0025] After being buffered in equalization tank 1, the aquaculture effluent is pumped by submersible pump 2 to the first-stage module. First, it passes through aeration and biochemical tank 31 to convert ammonia nitrogen into nitrate nitrogen. Then, it passes through biological filter bed 32 to filter recalcitrant nitrogenous substances and organic matter. Finally, it passes through a bacterial and algal biofilm unit to achieve deep removal of nitrate nitrogen and phosphorus. The effluent from the first-stage module (with significantly reduced pollutant concentration) serves as the influent to the second-stage module, entering the second-stage aeration, filtration, and bacterial / algal process for further removal of residual pollutants (such as low-concentration nitrate nitrogen and fine suspended particulate matter). This process continues until the second to fourth-stage modules complete the final purification. This approach breaks down the single-stage treatment of high-concentration pollutants into multiple progressive treatments of low-concentration pollutants, avoiding the incomplete treatment problems caused by excessively high pollutant concentrations and overloaded purification loads in traditional single-stage, large-volume treatment tanks.

[0026] Specifically, in some embodiments of the present invention, the thickness of the rice husk layer 321 in the biofilter bed 32 is 20-40cm, the thickness of the volcanic rock layer 322 is 40-60cm, and the rice husk layer 321 is located above the volcanic rock layer 322.

[0027] In this embodiment, the core function of the biofilter 32 is to provide an attachment and growth environment for microorganisms, promoting the synergistic operation of multiple purification mechanisms such as denitrification and microbial biodegradation within the system. It uses rice husk layer 321 and volcanic rock layer 322 as biological carriers, essentially utilizing the differentiated characteristics of these two materials to achieve progressive purification through physical interception and biodegradation. Considering the position of the biofilter 32 in the multi-stage coupled biochemical treatment unit 3 (after the aerated biochemical tank 31 and before the aerobic denitrifying microalgae biofilm unit 33), its treatment target is the effluent containing nitrate nitrogen, residual organic matter, and a small amount of suspended particulate matter after conversion in the aerated biochemical tank 31. The effluent enters from the top of the biofilter 32, first contacting the rice husk layer 321. Rice husk, as agricultural waste, has high porosity (>60%) and a large specific surface area, thus preferentially achieving the two main functions of physical interception and preliminary adsorption, as detailed below: Physical interception: Directly intercepts suspended particulate matter in the tailwater (such as uneaten feed and fecal particles in aquaculture tailwater, to prevent the pores of the volcanic rock layer 322 from being blocked by particulate matter and to ensure smooth water flow). Preliminary adsorption: Through surface adsorption, small-molecule organic matter (such as COD, influent concentration 52 mg / L) in the effluent is initially removed, reducing the biodegradation load on the subsequent volcanic rock layer. The thickness of the rice husk layer 321 is set at 20-40 cm, based on the balance between "adsorption capacity" and "flow resistance".

[0028] If the thickness is less than 20cm, the adsorption and interception capacity is insufficient and effective pretreatment is not possible; if the thickness is greater than 40cm, it will lead to increased water flow resistance, requiring an increase in the pump head and increased operating energy consumption.

[0029] The effluent, after pretreatment in the rice husk layer 321 (with suspended particulate matter and some organic matter removed), enters the lower volcanic rock layer 322. The volcanic rock has a rich pore structure (micropores and mesopores coexist), strong chemical stability, and good biocompatibility, enabling it to achieve two core functions: microbial attachment and denitrification. Microbial attachment: Provides sufficient attachment sites for functional microorganisms such as heterotrophic bacteria and denitrifying bacteria to form a stable biofilm. These microorganisms can further degrade residual organic matter in the effluent and reduce COD to a lower level. Denitrification: The anaerobic microenvironment of the volcanic rock layer 322 (where the water flow slows down after passing through the upper rice husk layer and a local anaerobic zone is formed in the lower layer) can promote the conversion of nitrate nitrogen produced in the aerated biological tank into nitrogen gas by denitrifying bacteria, which is a key step in "nitrate nitrogen removal" and lays the foundation for deep denitrification in the subsequent bacterial and algal biofilm unit.

[0030] Preferably, the thickness of the volcanic rock layer 322 is set to 40-60cm, based on the matching of "microbial residence time" and "degradation efficiency". If the thickness is <40cm, the microbial attachment area is insufficient, the denitrification reaction is incomplete, and the nitrate nitrogen removal rate is low; if the thickness is >60cm, although it can improve the degradation effect, it will increase the overall height of the filter bed, increase the system construction cost, and may also cause water flow short-circuiting, thus reducing the treatment efficiency.

[0031] Specifically, in some embodiments of the present invention, the microalgae 331 in the aerobic denitrifying microalgae biofilm unit 33 is at least one of Chlorella and Scenedesmus, and the initial inoculation concentration of microalgae 331 is 1×10⁻⁶. 6 -5×10 6 cells / mL.

[0032] The core function of the aerobic denitrifying microalgae biofilm unit is to form a "metabolic closed loop" with functional bacteria 332 (Bacillus wedmannii and Escherichia marmoseta). Microalgae 331 fixes CO2 and absorbs NH4 from the water through photosynthesis. + PO4 3-Nutrients are provided, and oxygen is released to support heterotrophic nitrification-aerobic denitrification by bacteria; the bacteria degrade organic matter to produce CO2, which feeds back to the microalgae 331, ultimately achieving efficient nitrogen and phosphorus removal without the need for external carbon sources.

[0033] Chlorella has the characteristics of high photosynthetic efficiency (light energy conversion rate can reach 5%-8%) and rapid reproduction rate (doubling time 24-36h), and can quickly absorb NH4 in water. + PO4 3- It has a wide range of adaptability to temperature (15-35℃) and light (1000-5000 lux) and can tolerate water quality fluctuations in aquaculture wastewater; Scenedesmus has a stable cell wall structure, strong resistance to pollution, and can secrete a small amount of antibacterial substances. At the same time, its colony growth characteristics can enhance the stability of the biofilm and prevent microalgal cells from being lost with the water flow.

[0034] The initial concentration of microalgae 331 can establish a symbiotic ratio of "microalgae:bacteria = 1:100-1:1000". At this ratio, the oxygen released by microalgae photosynthesis precisely meets the denitrification requirements of bacteria (per 1×10⁻⁶). 6 Each microalgal cell produces approximately 0.5 mg of oxygen per day, which can support 1×10⁻⁶ cells. 8 (aerobic metabolism of bacteria), while the CO2 produced by the bacteria (per 1×10) 8 Each bacterium produces approximately 1.2 mg of CO2 per day, which can be fully utilized by microalgae for photosynthesis, avoiding "excessive oxygen leading to energy waste" or "insufficient CO2 limiting microalgae growth", and ensuring the stable operation of the metabolic closed loop.

[0035] Specifically, in some embodiments of the present invention, the shellfish placed in the shellfish purification unit 4 are freshwater shellfish selected from at least one of freshwater mussels and razor clams, with a stocking density of 5-10 shellfish / m³. 3 .

[0036] By utilizing the filter-feeding behavior of shellfish, nutrients, suspended solids, organic particles, and inorganic particles are removed from the water. At the same time, nutrients absorbed by algae during their growth are transferred to the shellfish. After the shellfish mature, they are harvested as a byproduct, further purifying the water.

[0037] Freshwater mussels are typical freshwater shellfish, adapted to the aquatic environment of freshwater aquaculture areas (pH 6.5-8.5, water temperature 5-30℃), with a large filter feed capacity (the average daily water filtration capacity of a single adult freshwater mussel can reach 20-30L), and a rejection rate of more than 80% for tiny suspended particles (particle size 5-50μm) and microalgae, which can efficiently remove residual microalgae cells in the effluent of bacterial and algal units.

[0038] Although razor clams are commonly found in shallow seas, they can adapt to low-salinity freshwater environments (salinity < 5‰) after domestication. They also have the characteristics of being tolerant to low oxygen and growing quickly (they can mature in 6-8 months of cultivation). They can adapt to the water fluctuations in scattered aquaculture farms in mountainous areas (such as dissolved oxygen 2-8 mg / L). At the same time, their filter-feeding preferences complement those of freshwater mussels. Freshwater mussels focus on trapping large-diameter particles, while razor clams focus on adsorbing small-molecule organic debris. The combination of the two can achieve "interception of pollutants of all particle sizes".

[0039] Release density: 5-10 birds / m² 3 This can create a dynamic balance between feed supply and filter feed consumption.

[0040] Furthermore, in some other embodiments of the present invention, the wastewater treatment system further includes a microalgae biomass recovery unit 5, which is located at the sludge discharge port of the aerobic denitrifying microalgae biofilm unit 33 and is used for centrifugation, drying and recovery of microalgae biomass.

[0041] Microalgae absorb nitrogen and phosphorus, fix CO2, and form biomass through photosynthesis. During long-term operation, some aging microalgal cells and shed biofilm fragments will form algae-rich sludge. If this sludge is discharged directly, it will not only cause secondary loss of nitrogen and phosphorus (nitrogen and phosphorus are released again after the microalgae die), but also waste the resource value of microalgal biomass.

[0042] During stable operation, the biofilm thickness of the aerobic denitrifying microalgae biofilm unit will be maintained at 1-3 mm (to avoid excessive thickness leading to oxygen deficiency in the inner layer). When the microalgae reproduction rate exceeds the metabolic needs of the bacteria, some aging microalgae (growth cycle 7-10 days) will naturally detach, forming algae-rich sludge (approximately 95% water content, microalgae cell concentration ≥1×10⁻⁶) together with a small amount of bacterial residue and organic debris. 7 (cells / mL).

[0043] The microalgae biomass recovery unit 5 collects sludge through a directional sludge discharge port located at the bottom of the aerobic denitrification microalgae biofilm unit (the natural sludge settling area). It adopts a timed sludge discharge mode (1-2 times per week, with each discharge amount being 5%-10% of the unit volume). This avoids sludge accumulation in the unit, which could cause short-circuiting of the water flow, and ensures that the purity of microalgae in the collected sludge is ≥80% (reducing the impact of impurities on subsequent recovery).

[0044] The collected algae-rich sludge first enters a centrifuge, where high-speed centrifugation (3000-5000 r / min) achieves solid-liquid separation. This speed is designed based on the characteristics of microalgal cells: microalgal cells are approximately 5-10 μm in diameter, and the centrifugal force of 3000-5000 r / min allows the cells to settle rapidly, reducing the sludge moisture content from 95% to below 70% (forming an "algae cake"). Simultaneously, more than 70% of the free water in the sludge (containing a small amount of dissolved nitrogen and phosphorus, which can be returned to the equalization tank for reprocessing, avoiding resource waste) is removed.

[0045] After dehydration, the algal cake enters the drying equipment and is dried with low-temperature hot air (60-80℃). This temperature can retain more than 90% of the protein, vitamins and other nutrients in the microalgae (high temperature >100℃ will cause protein denaturation). Secondly, this temperature range ensures drying efficiency and reduces energy consumption. The resulting dried microalgae can be used directly to prepare aquatic feed (protein content 50%-60%) or further processed into bioenergy (such as anaerobic fermentation to produce biogas).

[0046] Furthermore, in some other embodiments of the present invention, a microporous aerator is installed in the aerated biological treatment tank 31, with an aeration intensity of 0.5-1.2 m. 3 / (m 2 •h), the residence time of the effluent in the aerated biological treatment tank 31 is ≥6h.

[0047] The aerated biological treatment tank 31 converts ammonia nitrogen in the aquaculture effluent into nitrate nitrogen through aerobic reaction, laying the foundation for the subsequent denitrification of the biological filter bed and the deep denitrification of the aerobic denitrification microalgae biofilm unit.

[0048] Microporous aerators feature small bubble diameters (1-3mm), large specific surface areas, and high dissolved oxygen efficiency (up to 20%-30%, far exceeding the 10%-15% of traditional perforated pipe aerators). Nitrifying bacteria (such as Nitrosomonas and Nitrifying Bacillus) are key functional bacteria for ammonia nitrogen conversion, and their metabolism requires sufficient dissolved oxygen (suitable dissolved oxygen concentration 2-4mg / L). The tiny bubbles generated by microporous aerators can remain in the water for a longer time (30-60s), allowing dissolved oxygen to diffuse evenly throughout the pool. This avoids the problems of insufficient dissolved oxygen in certain areas (bottom hypoxia) or excessive dissolved oxygen in certain areas (wasted aeration at the surface) associated with traditional aerators, ensuring consistent activity of nitrifying bacteria throughout the pool.

[0049] If traditional perforated tube aerators are used, a higher aeration intensity of 1.5-2.0m is required. 3 / (m 2 •h)) to achieve the same dissolved oxygen level, which will directly lead to increased aeration energy consumption.

[0050] Aeration intensity is a core parameter for controlling dissolved oxygen concentration, and the lower limit of aeration intensity ensures basic dissolved oxygen supply. When the influent ammonia nitrogen concentration is at a low level (e.g., <1 mg / L), 0.5 m 3 / (m 2 An aeration intensity of 1.2 m³ / h can maintain dissolved oxygen in the water ≥2 mg / L, meeting the minimum metabolic requirements of nitrifying bacteria and preventing incomplete ammonia nitrogen conversion (conversion efficiency <60%) due to insufficient dissolved oxygen; the upper limit of the aeration intensity can avoid energy waste and floc destruction. When the influent ammonia nitrogen concentration reaches its peak, 1.2 m³ / h 3 / (m 2 An aeration intensity of 1.2 m / h can raise dissolved oxygen to 3-4 mg / L, which is just enough to meet the high-efficiency metabolism of nitrifying bacteria (ammonia nitrogen conversion efficiency > 90%); if the intensity is > 1.2 m / h... 3 / (m 2 •h) will cause a sharp increase in energy consumption and excessive water flow disturbance, breaking up the bacterial flocs formed by nitrifying bacteria, which will reduce the conversion efficiency.

[0051] Furthermore, in some other embodiments of the present invention, the aerobic denitrifying microalgae biofilm unit 33 also includes a temperature control device 333 and a supplementary lighting device 334. The temperature control device 333 has a control temperature range of 15-30°C, and the supplementary lighting device 334 has a light intensity of 2000-5000 lux.

[0052] In this embodiment, microalgae fix CO2 and absorb NH4 through photosynthesis. + PO4 3- The bacteria release oxygen, which they then use to perform heterotrophic nitrification-aerobic denitrification to degrade nitrogen compounds, while simultaneously producing CO2 to feed the microalgae. The efficiency of photosynthesis directly depends on temperature and light intensity, and the bacterial denitrification activity is also significantly affected by temperature. Therefore, by using temperature control and supplemental lighting devices, the interference of environmental temperature and light fluctuations on the symbiotic system can be eliminated, ensuring the continuous stability of the metabolic closed loop and providing a guarantee for efficient nitrogen and phosphorus removal without external carbon sources.

[0053] Temperature control device 333 maintains the water temperature in the unit at 15-30℃ by heating (in winter) or dissipating heat (in summer), a range determined based on the physiological characteristics of microalgae and functional bacteria; supplementary lighting device 334 (usually an LED light source) is activated when natural light is insufficient (such as on cloudy days, at night, or in indoor aquaculture scenarios) to maintain the light intensity at 2000-5000 lux, a range designed based on the photosynthetic characteristics of microalgae.

[0054] Please see Figure 3 As shown in the figure, this embodiment of the invention also provides a method for treating aquaculture wastewater using an integrated system of bacteria and algae symbiosis, the method comprising the following steps: S1: Wastewater buffer. Aquaculture wastewater is discharged into the equalization tank to homogenize the water quality. The buffering time is 2-4 hours.

[0055] In this step, the aquaculture wastewater (such as pond drainage) experiences fluctuations in water quality and quantity. Directly entering the downstream treatment unit can easily lead to shock loads (such as a sudden drop in the activity of nitrifying bacteria in the aerated biological treatment tank). A buffer time of 2-4 hours can basically eliminate short-term fluctuations (such as a drop in ammonia nitrogen from 3 mg / L to 2.4 mg / L), and 4 hours can cope with larger fluctuations (such as a 50% increase in water volume during the rainy season).

[0056] S2: Aerobic conversion. The submersible pump transports the effluent from the equalization tank to the aerated biological treatment tank. Under aeration conditions, the reaction lasts for 6-12 hours, converting ammonia nitrogen into nitrate nitrogen.

[0057] In this step, nitrifying bacteria are used to convert ammonia nitrogen into nitrate nitrogen. The cycle of nitrifying bacteria converting ammonia nitrogen into nitrate nitrogen is about 4-6 hours. More than 90% conversion can be achieved in 6 hours (effluent ammonia nitrogen ≤0.3mg / L), and 12 hours can handle high ammonia nitrogen influent (such as 3mg / L). The reaction time of 6-12 hours ensures that dissolved oxygen and bacterial metabolic needs are matched, so that the conversion will not be stopped due to insufficient aeration, nor will excessive aeration waste energy.

[0058] S3: Biological filtration. The effluent from the aerated biological treatment tank enters the biological filter bed, where it is adsorbed by the rice husk layer and degraded by microorganisms in the volcanic rock layer, removing recalcitrant nitrogenous substances and organic matter.

[0059] In this step, the rice husk layer acts as a pre-interceptor, preferentially adsorbing suspended matter and preventing clogging of the pores in the volcanic rock layer; at the same time, the rice husk slowly degrades and releases small molecule carbon sources (such as organic acids), alleviating the carbon source shortage problem in the aquaculture wastewater with a C / N ratio of <5.

[0060] Volcanic rock provides attachment sites for denitrifying bacteria, converting nitrate nitrogen (2-2.5 mg / L) produced by S2 into nitrogen gas (removal rate 60%-70%), while degrading residual COD (from 52 mg / L to below 20 mg / L), reducing the load on subsequent bacterial-algae symbiotic degradation.

[0061] S4: Algal-microbe symbiotic degradation. The effluent from the biofilter enters the aerobic denitrification microalgae biofilm unit, where it is circulated and degraded for 6-10 hours at 15-30℃ and 2000-5000 lux, achieving nitrogen and phosphorus removal.

[0062] In this step, for the effluent from step S3 (containing residual nitrate nitrogen, phosphorus, and trace organic matter), deep purification is achieved through the symbiotic relationship between microalgae (Chlorella / Scenedesmus) and functional bacteria (Bacillus wedemannii, Escherichia coli): 15-30℃ can maintain the activity of bacteria and algae, at which time the photosynthetic efficiency of microalgae is the highest and the denitrification activity of bacteria is the best; 2000-5000 lux can ensure that microalgae photosynthesize oxygen and provide energy for bacterial denitrification; microalgae need more than 6 hours to absorb phosphorus, and bacteria need more than 8 hours to convert residual nitrate nitrogen into nitrogen gas.

[0063] S5: Shellfish purification. The effluent from the aerobic denitrification microalgae biofilm unit enters the shellfish purification unit and is treated for 4-8 hours before being discharged in compliance with standards or recycled.

[0064] This wastewater treatment method gradually transforms highly polluted aquaculture wastewater into compliant water, while simultaneously achieving low energy consumption, resource utilization, no secondary pollution, improved purification efficiency, and reduced operating energy consumption.

[0065] Furthermore, in some other embodiments of the present invention, in step S4, the inoculation ratio of microalgae to functional bacteria in the aerobic denitrifying microalgae biofilm unit is (1×10⁻⁶). 6 -5×10 6 cells / mL): (1×10 8 -5×10 8 (CFU / mL).

[0066] In this step, microalgae fix CO2 and absorb NH4 through photosynthesis. + PO4 3- It releases oxygen, and the functional bacteria (Bacillus wedemannii and Escherichia marmoseta) rely on oxygen to carry out heterotrophic nitrification-aerobic denitrification, degrading nitrogen compounds while producing CO2 to feed back to the microalgae, ultimately achieving efficient nitrogen and phosphorus removal without the need for external carbon sources.

[0067] The bacterial-algae inoculation ratio is based on the quantitative matching relationship between "microalgae oxygen production capacity" and "bacterial oxygen consumption demand", "bacterial CO2 production" and "microalgae carbon fixation demand", to avoid disrupting the symbiotic balance due to excess or deficiency of one side, and to provide quantitative support for the stable operation of the metabolic closed loop.

[0068] Furthermore, in some other embodiments of the present invention, the aquaculture wastewater treatment method further includes step S6: resource recovery; Algae-rich sludge is periodically discharged from the aerobic denitrifying microalgae biofilm unit, and the microalgae biomass is recovered through centrifugation and drying; shellfish are harvested as by-products after they mature.

[0069] In this step, the aerobic denitrifying microalgae biofilm unit will generate algae-rich sludge during operation, and the shellfish in shellfish purification unit 4 will accumulate biomass by filtering microalgae and particulate matter. If these purification byproducts are directly discharged, it will not only cause secondary loss of nitrogen and phosphorus (nitrogen and phosphorus are released after the microalgae die), but also waste the high protein value of microalgae and the economic value of shellfish.

[0070] By transforming pollution control byproducts into usable resources and through a dual approach of microalgae biomass recycling and shellfish harvesting, the pollution control costs can be converted into economic benefits.

[0071] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A symbiotic aquaculture wastewater treatment system, characterized in that, It includes an equalization tank, submersible pumps, a multi-stage coupled biochemical treatment unit, and a shellfish purification unit; The submersible pump is located at the outlet of the equalization tank and is used to transport the effluent to the multi-stage coupled biological treatment unit. The multi-stage coupled biological treatment unit includes an aerated biological treatment tank, a biological filter bed, and an aerobic denitrifying microalgae biofilm unit connected in series. The biological filter bed uses rice husk layer and volcanic rock layer as biological carriers. The aerobic denitrifying microalgae biofilm unit contains microalgae and functional bacteria. The functional bacteria are Bacillus widmannii and Escherichia coli. The microalgae fix CO2 and release oxygen through photosynthesis, and the functional bacteria degrade nitrogen oxides through heterotrophic nitrification-aerobic denitrification. The shellfish purification unit is located at the outlet of the multi-stage coupled biological treatment unit and is used to filter residual microalgae and suspended particulate matter in the water.

2. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, The multi-stage coupled biochemical processing unit consists of 2-4 stages in series, with a single module processing capacity of 20-50m³. 3 / sky.

3. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, The rice husk layer in the biofilter bed is 20-40cm thick, the volcanic rock layer is 40-60cm thick, and the rice husk layer is located above the volcanic rock layer.

4. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, The microalgae in the aerobic denitrifying microalgae biofilm unit are at least one of Chlorella and Scenedesmus, and the initial inoculum concentration of the microalgae is 1×10⁻⁶. 6 -5×10 6 cells / mL.

5. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, The shellfish introduced into the shellfish purification unit are freshwater shellfish selected from at least one of freshwater mussels and razor clams, with a stocking density of 5-10 shellfish / m². 3 .

6. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, It also includes a microalgae biomass recovery unit, which is located at the sludge discharge port of the aerobic denitrification microalgae biofilm unit and is used for centrifugation, drying and recovery of microalgae biomass.

7. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, The aerated biological treatment tank is equipped with microporous aerators, with an aeration intensity of 0.5-1.2 m. 3 / (m 2 •h), the residence time of the effluent in the aerated biological treatment tank is ≥6h.

8. The integrated aquaculture wastewater treatment system based on algae and bacteria symbiosis according to claim 1, characterized in that, The aerobic denitrifying microalgae biofilm unit also includes a temperature control device and a supplemental lighting device. The temperature inside the control unit is 15-30℃ and the light intensity is 2000-5000 lux.

9. A method for treating wastewater from an integrated aquaculture system based on any one of claims 1-8, characterized in that, Includes the following steps: S1: Wastewater buffer, aquaculture wastewater is discharged into the equalization tank to homogenize the water quality, and the buffering time is 2-4 hours; S2: Aerobic conversion. The submersible sewage pump transports the effluent from the equalization tank to the aerated biological treatment tank. Under aeration conditions, the reaction lasts for 6-12 hours, converting ammonia nitrogen into nitrate nitrogen. S3: Biological filtration. The effluent from the aerated biological treatment tank enters the biological filter bed, where it is adsorbed by the rice husk layer and degraded by microorganisms in the volcanic rock layer to remove recalcitrant nitrogenous substances and organic matter. S4: Algal-microbe symbiotic degradation. The effluent from the biofilter enters the aerobic denitrification microalgae biofilm unit, where it is circulated and degraded for 6-10 hours at 15-30℃ and 2000-5000 lux, achieving nitrogen and phosphorus removal. S5: Shellfish purification. The effluent from the aerobic denitrification microalgae biofilm unit enters the shellfish purification unit and is treated for 4-8 hours before being discharged in compliance with standards or recycled.

10. The method for treating wastewater from integrated aquaculture with bacteria and algae symbiosis according to claim 9, characterized in that, In step S4, the inoculation ratio of microalgae to functional bacteria in the aerobic denitrifying microalgae biofilm unit is (1×10⁻⁶). 6 -5×10 6 cells / mL): (1×10 8 -5×10 8 (CFU / mL).

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