A grass carp recirculating aquaculture effluent comprehensive treatment system based on MABR and a use method thereof

Abstract

The present application relates to a kind of grass carp circulating water aquaculture tail water comprehensive treatment system based on MABR and its use method, it relates to aquaculture water treatment technical field.Processing system is sequentially connected physical filtration unit, biological filtration unit, MABR processing unit, disinfection unit and reuse unit, air supply unit is separately arranged;Use method is to apply MABR technology to biological filtration unit after, before disinfection unit, utilize physical filtration unit to remove large particle impurities and part of suspended solids in water body, the microorganism attached to biological filter material in biological filter carries out biological degradation to organic matter, ammonia nitrogen and other pollutants in water body, the microorganism attached to MABR membrane in MABR processing unit carries out depth degradation to the pollutants in water body, again, to the water body after treatment ultraviolet disinfection is killed pathogenic microorganism, subsequent water body oxygenation recycling or discharge is discharged.The present application has integrated technology removal effect, good stability, save external carbon source and other advantages.

Description

Technical Field

[0001] This invention relates to the field of aquaculture water treatment technology, specifically to a comprehensive treatment system for grass carp recirculating aquaculture wastewater based on MABR and its application method. Background Technology

[0002] Recirculating aquaculture systems (RAS) are a highly efficient and sustainable aquaculture model that significantly reduces water consumption and environmental pollution by recycling aquaculture water. They purify the aquaculture water through a series of water treatment units, such as biofilters, protein skimmers, and ultraviolet disinfectors, bringing it to a standard suitable for reuse, thus achieving water resource recycling. However, despite these advantages, RAS faces several challenges in practical application, including insufficient water quality stability, high energy consumption, large footprint, and complex maintenance. These issues limit the widespread application and further development of RAS.

[0003] Membrane aerated biofilm reactor (MABR) technology has gained widespread attention in wastewater treatment due to its high efficiency, energy saving, and environmental friendliness. The MABR process forms a biofilm on the membrane surface, utilizing the property of oxygen permeability to provide oxygen to the microorganisms within the biofilm, thereby achieving efficient degradation of organic matter and nitrogen in wastewater. Currently, the application of MABR technology in recirculating aquaculture systems is mainly concentrated in single-stage applications, such as as a replacement or supplementary unit to biological filters. This single-stage application approach fails to fully leverage the comprehensive advantages of the MABR process and still has some problems, such as insufficient system integration, inadequate optimization of operating parameters, and insufficient intelligent control.

[0004] In conclusion, by implementing a MABR-based integrated wastewater treatment system for grass carp recirculating aquaculture, along with its application methods, optimized operating parameters, and the inclusion of an intelligent control system, efficient water purification and stable maintenance can be achieved, while simultaneously reducing system energy consumption and operating costs. This not only helps improve the overall performance and economic benefits of recirculating aquaculture systems but also provides strong support for the sustainable development of the aquaculture industry. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a comprehensive treatment system for grass carp recirculating aquaculture wastewater based on MABR and its application method. The MABR technology is applied after the biological filtration unit and before the disinfection unit, thereby improving the quality of the effluent and meeting the discharge requirements to a high standard.

[0006] This invention is achieved through the following techniques: A comprehensive treatment system for grass carp recirculating aquaculture wastewater based on MABR is characterized by the sequential connection of a physical filtration unit, a biological filtration unit, a MABR treatment unit, a disinfection unit, and a reuse unit, with a separate air supply unit, mainly including air supply equipment, air supply pipelines, valves, and a frequency conversion control and monitoring system. The physical filtration unit includes one or more of a solid-liquid separator, an arc screen, or a protein separator; The biological filtration unit adopts a double-layer vertical upflow biological filter, with a microporous aeration device at the bottom, and the lower layer is filled with a specific surface area of ​​60-100 m². 2 / g porous ceramsite, with an upper layer filled with one or both of volcanic rock and bioceramics, and a specific surface area greater than 100m². 2 / g; The MABR treatment unit is located after the biofiltration unit and before the disinfection unit. It mainly consists of a MABR membrane tank, an air supply connection pipe, and a bottom purging system. The MABR membrane tank has a filling rate of 20% to 45%. The bottom purging system consists of an air supply pipe, valves, and a perforated purging pipe. The purging pipe has purging holes with a diameter of 1.5-2 mm and a spacing of 100 mm between the purging holes. The disinfection unit is equipped with an ultraviolet disinfection device. The gas supply unit provides oxygen to the protein separator, biofiltration unit, MABR treatment unit, and recycling unit in the physical filtration unit, respectively, and the frequency conversion control monitoring system monitors the dissolved oxygen concentration in the biofiltration unit and the MABR treatment unit.

[0007] Furthermore, the outer surface of the membrane fibers of the MABR membrane module inside the MABR membrane box is covered with microorganisms such as nitrifying bacteria, denitrifying bacteria, nitrite-oxidizing bacteria, and polyphosphate-accumulating bacteria. In the initial stage of operation, the ratio of microbial inoculation is 1:1 to 3:1 for nitrifying bacteria and denitrifying bacteria, and the ratio of the total inoculation of nitrite-oxidizing bacteria and polyphosphate-accumulating bacteria to the total inoculation of nitrifying bacteria and denitrifying bacteria is 1:1 to 2:1.

[0008] Furthermore, the ultraviolet wavelength of the ultraviolet disinfection device is 250-280nm, and the power of the ultraviolet disinfection device is 1-5kW.

[0009] The specific operating steps for using the above processing system are as follows: (1) Wastewater collection and pretreatment: The wastewater discharged from the grass carp breeding pond is piped into the physical filtration unit, and passes through the solid-liquid separator, arc screen and / or protein separator in sequence to remove solid particles with a particle size greater than 80μm, uneaten feed, feces and some organic suspended matter in the water to obtain pretreated water. (2) Biological filtration treatment: The pretreated water is pumped into a double-layer vertical upflow biological filter. The water flows from bottom to top. The dissolved oxygen concentration in the lower layer is controlled at 2 mg / L, and the dissolved oxygen concentration in the upper layer is controlled at 0.5 mg / L. Nitrification occurs in the lower layer, and autotrophic denitrification is achieved in the upper layer to remove total nitrogen. (3) MABR membrane treatment: The biologically filtered water is fed into the MABR treatment unit by gravity flow. The air supply system intermittently supplies oxygen to the MABR membrane tank. The surface of the membrane fibers is covered with a complex of microorganisms such as nitrifying bacteria, denitrifying bacteria, nitrite-oxidizing bacteria, and polyphosphate-accumulating bacteria. The frequency conversion control and monitoring system controls the intermittent air supply and monitors the dissolved oxygen concentration in the treatment unit. The intermittent air supply cycle is 1 hour, divided into an air supply section and an air stop section. The air supply section lasts for 20 minutes, with the air supply pressure of the MABR membrane tank at 15 kPa~25 kPa and the dissolved oxygen concentration at 1.5-2.0 mg / L. The biofilm on the outer surface of the MABR membrane fibers achieves simultaneous nitrification and denitrification. The air stop section lasts for 40 minutes, during which the MABR membrane tank stops supplying air, and the dissolved oxygen concentration does not exceed 0.4 mg / L. The denitrification of the biofilm on the outer surface of the MABR membrane fibers continues, degrading NO3. - -N; The bottom purging system is activated within 5-10 seconds at the start of the second gas supply cycle to purge the biofilm, maintaining the biofilm thickness at no more than 200μm. (4) Ultraviolet disinfection treatment: The water treated by the MABR membrane is introduced into the ultraviolet disinfection device by gravity flow, and the irradiation time is 10-30s to kill pathogenic microorganisms in the water. (5) Wastewater reuse or discharge: After the disinfected water is aerated and oxygenated, it is returned to the recirculating aquaculture system to realize the recycling of the water, or it is directly discharged into natural water bodies after meeting the discharge standards.

[0010] This invention discloses a comprehensive treatment system for grass carp recirculating aquaculture wastewater based on MABR (Magnetic Recirculating Bioreactor) technology and its application method. Addressing the relatively low carbon-to-nitrogen ratio in aquaculture wastewater, the MABR technology is integrated with physical filtration, biological filtration, and disinfection units instead of replacing the biological filtration unit. The physical filtration unit removes large particulate impurities and some suspended solids. Microorganisms attached to the biological filter media in the biological filter biodegrade pollutants such as organic matter and ammonia nitrogen. Microorganisms attached to the MABR membrane in the MABR treatment unit further degrade pollutants. The treated water is then disinfected with ultraviolet light to kill pathogenic microorganisms, followed by oxygenation and recycling or discharge to meet standards. This invention offers advantages such as good removal efficiency, high stability, and conservation of external carbon sources through integrated technology. Detailed Implementation

[0011] The following examples systematically illustrate the technical concept, implementation effects, and inventive intent of this invention, so as to fully understand its innovative value.

[0012] A comprehensive treatment system for grass carp recirculating aquaculture wastewater based on MABR (Maintenance, Bioreactor, and Biofilter) is sequentially connected to a physical filtration unit, a biological filtration unit, a MABR treatment unit, a disinfection unit, and a reuse unit. The air supply unit is separately configured and mainly includes air supply equipment, air supply pipelines, valves, and a frequency converter control and monitoring system. The physical filtration unit includes one or more of a solid-liquid separator, an arc screen, or a protein skimmer, such as a solid-liquid separator + protein skimmer, an arc screen + protein skimmer, or a solid-liquid separator + arc screen + protein skimmer. The biological filtration unit adopts a double-layer vertical upflow biological filter with a microporous aeration device at the bottom, and the lower layer has a specific surface area of ​​60-100 m². 2 / g porous ceramsite, such as porous ceramsite with a specific surface area of ​​60, 80, 90 or 100m² 2 / g, etc., with an upper layer filled with one or both of volcanic rock and bioceramics, and a specific surface area greater than 100m². 2 / g, such as volcanic rock or bioceramic or a combination of volcanic rock and bioceramic filter media; the MABR treatment unit is located after the biofiltration unit and before the disinfection unit, mainly composed of a MABR membrane box, an air supply connection pipe, and a bottom purging system. The MABR membrane box has a filling rate of 20%~45%. The bottom purging system consists of an air supply pipe, valves, and a perforated purging pipe. The purging pipe has purging holes with a diameter of 1.5-2mm and a spacing of 100mm. The disinfection unit is equipped with an ultraviolet disinfection device. The air supply unit supplies oxygen to the protein separator, biofiltration unit, MABR treatment unit, and reuse unit in the physical filtration unit. The frequency conversion control monitoring system monitors the dissolved oxygen concentration in the biofiltration unit and the MABR treatment unit.

[0013] The MABR membrane module inside the membrane chamber has microorganisms such as nitrifying bacteria, denitrifying bacteria, nitrite-oxidizing bacteria, and polyphosphate-accumulating bacteria attached to its outer surface. During the initial operation phase, the inoculum ratio of nitrifying bacteria to denitrifying bacteria is 1:1-3:1, and the inoculum ratio of nitrite-oxidizing bacteria and polyphosphate-accumulating bacteria to the total of nitrifying and denitrifying bacteria is 1:1-2:1. The ultraviolet wavelength of the ultraviolet disinfection device is 250-280nm, and the power of the ultraviolet disinfection device is 1-5kW.

[0014] Example: Freshwater high-density grass carp farming system scale: 100m³ aquaculture water volume, 30kg / m³ grass carp stocking density, and daily water exchange of 80% of the aquaculture water volume (i.e., daily effluent treatment volume of 80m³). Initial effluent water quality: Initial effluent was monitored for 7 consecutive days, and the average indicators were determined to be: COD 95±3mg / L, ammonia nitrogen 14.5±0.8mg / L, nitrite 1.1±0.1mg / L, and suspended solids 39±2mg / L. Common process parameters: The physical filtration unit of the original treatment system adopted a combination of "solid-liquid separator + arc screen + protein separator". The biological filter was filled with porous ceramic granules (specific surface area 90m² / g) and volcanic rock filter media (specific surface area 120m² / g). The disinfection unit had the following parameters: wavelength 265nm, power 3kW, system hydraulic retention time controlled at 4h, operating temperature stable at 25±2℃, and pH maintained at 7.2-7.5. The microbial inoculation ratio is "nitrifying bacteria: denitrifying bacteria = 2:1, nitrite + polyphosphate-accumulating bacteria: (nitrifying bacteria + denitrifying bacteria) = 1.5:1". The original treatment process did not have a MABR treatment unit, and the process flow was physical filtration unit → biological filtration unit → disinfection unit → reuse unit.

[0015] A new MABR treatment unit was added, with the following parameters: 4 MABR membrane tanks, 40% fill rate; 2mm orifice holes with a spacing of 100mm on the purge pipe of the bottom purge system; initial microbial inoculum ratio of "nitrifying bacteria: denitrifying bacteria = 2:1, nitrite + polyphosphate-accumulating bacteria: (nitrifying bacteria + denitrifying bacteria) = 1.5:1". The MABR treatment unit was operated and controlled as follows: intermittent gas supply cycle of 1 hour, divided into a supply phase and a stop phase; the supply phase lasted 20 minutes, with a gas supply pressure of 20 kPa and dissolved oxygen concentration of 1.5-2.0 mg / L, achieving simultaneous nitrification and denitrification of the biofilm on the outer surface of the MABR membrane fibers; the stop phase lasted 40 minutes, during which the MABR membrane tank stopped supplying gas, with a dissolved oxygen concentration of 0.2-0.4 mg / L, and denitrification of NO3 continued on the outer surface of the MABR membrane fibers. - -N; The bottom purging system is activated within 5 seconds at the start of the second air supply cycle to purge the biofilm, maintaining the biofilm thickness at no more than 200μm; The hydraulic retention time of the treatment unit is adjusted at any time according to the fluctuation of the effluent quality, and controlled at 6~10h.

[0016] Comparative Example 1: The MABR treatment unit is located after the physical filtration unit and before the biological filtration unit. The process flow is: physical filtration unit → MABR treatment unit → biological filtration unit → disinfection unit → reuse unit.

[0017] Comparative Example 2: The difference from Comparative Example 1 is that the MABR treatment unit is set after the biological filtration unit and before the disinfection unit. The process flow is physical filtration unit → biological filtration unit → MABR treatment unit → disinfection unit → reuse unit.

[0018] Comparative Example 3: The difference from Comparative Example 2 is that the distance between the MABR treatment unit and the disinfection unit is shortened to 1m to verify the effect of positional difference; the process flow is physical filtration unit → biological filtration unit → MABR treatment unit (adjacent to the disinfection unit) → disinfection unit → reuse unit.

[0019] The system was run continuously for 30 days. Samples were taken daily at the outlet of each system (after UV disinfection). The average value over 30 days was used as the final data. The compliance status was judged by referring to the "Recycled Water Reuse Standard" (COD≤15mg / L, ammonia nitrogen≤0.8mg / L, nitrite≤0.1mg / L, suspended solids≤5mg / L) in the "Freshwater Pond Aquaculture Water Discharge Standard" (GB11607-2000).

[0020] Traditional systems rely solely on microbial degradation in biological filters, which become saturated with the ability to degrade low-concentration pollutants (such as COD < 30 mg / L and ammonia nitrogen < 5 mg / L), leading to effluent exceeding standards. In contrast, MABR provides sufficient oxygen to microorganisms through membrane aeration, enhancing nitrification, denitrification, and organic matter mineralization processes, thus significantly improving removal efficiency.

[0021] In Comparative Example 1, the MABR membrane treatment unit directly treated the effluent after physical filtration. At this point, the water still contained a significant amount of suspended solids (approximately 15-20 mg / L), which easily adhered to the MABR membrane surface, causing membrane fouling. This resulted in a decrease in the efficiency of contact between microorganisms and pollutants, leading to a 7.5%-7.3% lower COD and ammonia nitrogen removal rates compared to Comparative Example 2. In Comparative Examples 2 and 3, biological filtration had already pre-removed some suspended solids and organic matter, allowing microorganisms to degrade the remaining low-concentration pollutants more efficiently, resulting in superior effluent indicators. The only difference between Comparative Examples 2 and 3 was the spacing between the MABR and the ultraviolet disinfection unit. The compact layout of Comparative Example 3 reduced secondary pollution during water transport (such as a slight increase in COD due to microbial growth on the inner wall of the pipe), thus further reducing COD and ammonia nitrogen by 0.2-0.3 mg / L and suspended solids by 0.3 mg / L, validating the optimization value of "MABR adjacent to the disinfection unit."

[0022] In summary, it can be seen that the application location of the MABR treatment unit significantly affects the effluent purification effect in high-density freshwater grass carp farming. The optimal application location is after the biological filtration unit and before the disinfection unit (especially in Example 3 with a compact layout of the MABR treatment unit and disinfection unit), achieving a COD removal rate of 87.1%, an ammonia nitrogen removal rate of 96.6%, and a nitrite removal rate of 96.4%, with the effluent fully meeting reuse standards. This application location can synergize with the biological filtration unit, utilizing pretreatment to reduce membrane fouling while achieving deep purification through the MABR treatment unit, balancing purification effectiveness and operational stability, and providing a reliable technical solution for recirculating water reuse in high-density freshwater grass carp farming.

[0023] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A comprehensive wastewater treatment system for grass carp recirculating aquaculture systems based on MABR, characterized in that, The system is connected in sequence to the physical filtration unit, biological filtration unit, MABR treatment unit, disinfection unit, and reuse unit. The gas supply unit is set up separately and mainly includes gas supply equipment, gas supply pipelines, valves, and frequency conversion control and monitoring system. The physical filtration unit includes one or more of a solid-liquid separator, an arc screen, or a protein separator; The biological filtration unit adopts a double-layer vertical upflow biological filter, with a microporous aeration device at the bottom, and the lower layer is filled with a specific surface area of ​​60-100 m². 2 / g porous ceramsite, with an upper layer filled with one or both of volcanic rock and bioceramics, and a specific surface area greater than 100m². 2 / g; The MABR treatment unit is located after the biofiltration unit and before the disinfection unit. It mainly consists of a MABR membrane tank, an air supply connection pipe, and a bottom purging system. The MABR membrane tank has a filling rate of 20% to 45%. The bottom purging system consists of an air supply pipe, valves, and a perforated purging pipe. The purging pipe has purging holes with a diameter of 1.5-2 mm and a spacing of 100 mm between the purging holes. The disinfection unit is equipped with an ultraviolet disinfection device. The gas supply unit provides oxygen to the protein separator, biofiltration unit, MABR treatment unit, and recycling unit in the physical filtration unit, respectively, and the frequency conversion control monitoring system monitors the dissolved oxygen concentration in the biofiltration unit and the MABR treatment unit.

2. The integrated treatment system for grass carp recirculating aquaculture wastewater based on MABR as described in claim 1, characterized in that: The outer surface of the MABR membrane module in the MABR membrane box is covered with microorganisms such as nitrifying bacteria, denitrifying bacteria, nitrite-oxidizing bacteria and polyphosphate-accumulating bacteria. In the initial stage of operation, the ratio of microbial inoculum is 1:1 to 3:1 for nitrifying bacteria and denitrifying bacteria, and the ratio of nitrite-oxidizing bacteria and polyphosphate-accumulating bacteria to the total amount of nitrifying bacteria and denitrifying bacteria is 1:1 to 2:

1.

3. The integrated treatment system for grass carp recirculating aquaculture wastewater based on MABR as described in claim 1, characterized in that: The ultraviolet wavelength of the ultraviolet disinfection device is 250-280nm, and the power of the ultraviolet disinfection device is 1-5kW.

4. A method for using the MABR-based grass carp recirculating aquaculture wastewater integrated treatment system as described in claims 1-3, characterized in that: The specific operating steps are as follows: (1) Wastewater collection and pretreatment: The wastewater discharged from the grass carp breeding pond is piped into the physical filtration unit, and passes through the solid-liquid separator, arc screen and / or protein separator in sequence to remove solid particles with a particle size greater than 80μm, uneaten feed, feces and some organic suspended matter in the water to obtain pretreated water. (2) Biological filtration treatment: The pretreated water is pumped into a double-layer vertical upflow biological filter. The water flows from bottom to top. The dissolved oxygen concentration in the lower layer is controlled at 2 mg / L, and the dissolved oxygen concentration in the upper layer is controlled at 0.5 mg / L. Nitrification occurs in the lower layer, and autotrophic denitrification is achieved in the upper layer to remove total nitrogen. (3) MABR membrane treatment: The biologically filtered water is fed into the MABR treatment unit by gravity flow. The air supply system intermittently supplies oxygen to the MABR membrane tank. The surface of the membrane fibers is covered with a complex of microorganisms such as nitrifying bacteria, denitrifying bacteria, nitrite-oxidizing bacteria, and polyphosphate-accumulating bacteria. The frequency conversion control and monitoring system controls the intermittent air supply and monitors the dissolved oxygen concentration in the treatment unit. The intermittent air supply cycle is 1 hour, divided into an air supply section and an air stop section. The air supply section lasts for 20 minutes, with the air supply pressure of the MABR membrane tank at 15 kPa~25 kPa and the dissolved oxygen concentration at 1.5-2.0 mg / L. The biofilm on the outer surface of the MABR membrane fibers achieves simultaneous nitrification and denitrification. The air stop section lasts for 40 minutes, during which the MABR membrane tank stops supplying air, and the dissolved oxygen concentration does not exceed 0.4 mg / L. The denitrification of the biofilm on the outer surface of the MABR membrane fibers continues, degrading NO3. - -N; The bottom purging system is activated within 5-10 seconds at the start of the second gas supply cycle to purge the biofilm, maintaining the biofilm thickness at no more than 200μm. (4) Ultraviolet disinfection treatment: The water treated by the MABR membrane is introduced into the ultraviolet disinfection device by gravity flow, and the irradiation time is 10-30s to kill pathogenic microorganisms in the water. (5) Wastewater reuse or discharge: After the disinfected water is aerated and oxygenated, it is returned to the recirculating aquaculture system to realize the recycling of the water, or it is directly discharged into natural water bodies after meeting the discharge standards.