Straw-based biofilm carrier, preparation method and application thereof

Abstract

The present application relates to sewage treatment technical field, more specifically, the present application relates to a kind of straw-based biofilm carrier and its preparation method and application.The present application provides a kind of straw-based biofilm carrier and its preparation method, and with crop straw as film-hanging carrier, construct algal-bacterial symbiotic system and be applied to aquaculture tail water treatment.Straw can be used as the carrier filler for the growth of microalgae and bacteria on the one hand, and can slowly release organic matter as carbon source for the growth of microorganisms attached thereto during degradation on the other hand.Microalgae photosynthesis can provide oxygen for aerobic bacteria, and the present application does not need aeration when treating aquaculture tail water, and the aged biofilm on straw is periodically peeled off by water flow impact and collected as fish bait, while treating aquaculture tail water, the organic matter and nitrogen, phosphorus and other nutrients therein can be recycled and utilized.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology. More specifically, this invention relates to a straw-based biofilm carrier, its preparation method, and its application. Background Technology

[0002] my country is a major aquaculture country with a large aquaculture area, high yield, and diverse aquaculture species. In recent years, with the rapid development of high-density aquaculture, the ecological and environmental problems caused by aquaculture wastewater discharge have become increasingly prominent. Aquaculture wastewater refers to wastewater containing pollutants such as waste, aquaculture residues, feces, feed residues, and aquaculture drugs generated during or after aquaculture. Excessive nitrogen and phosphorus nutrients in aquaculture wastewater can cause eutrophication of surrounding natural waters, seriously affecting the surrounding ecological environment. High concentrations of ammonia nitrogen and nitrite can damage the tissue structure, physiological characteristics, and metabolic capacity of farmed organisms, leading to mass mortality of aquatic products. Traditional aquaculture wastewater treatment technologies mainly include physical, chemical, and biological treatment methods. Among them, physical and chemical methods, such as adsorption filtration, flocculation sedimentation, and ozone oxidation, play an important role in water body restoration. However, high energy consumption, excessive waste sludge, and large amounts of greenhouse gas emissions limit the use of these methods. In contrast, biological treatment technology utilizes the metabolic capacity of microorganisms or autotrophic plants to convert pollutants into energy, which not only reduces pollutant emissions but also provides the possibility of restoring damaged ecosystems, demonstrating its advantages of being environmentally friendly, safe, and low in toxicity.

[0003] Generally, using microorganisms to remove nitrogen is a relatively economical method. Microorganisms convert organic nitrogen in water into nitrogen gas through nitrification and denitrification. Denitrifying bacteria play an important role in biological nitrogen removal. These bacteria are usually heterotrophic organisms, and their denitrification requires a sufficient organic carbon source. However, the concentration of organic matter in aquaculture wastewater is usually low, with COD between 20 mg / L and 100 mg / L, which cannot meet the nitrogen removal needs of denitrifying bacteria, resulting in low biological nitrogen removal efficiency in aquaculture wastewater. Microalgae are a type of single-celled microorganism that grows rapidly, has simple nutritional requirements, and is easy to cultivate. Microalgae use light as an energy source and absorb elements such as carbon, nitrogen, and phosphorus from aquaculture wastewater to provide themselves with nutrients. They can effectively remove pollutants such as nitrogen and phosphorus and further realize resource utilization. Although microalgae have a strong ability to absorb and assimilate nitrogen and phosphorus pollutants in aquaculture wastewater, using microalgae alone to treat wastewater is often ineffective. Firstly, microalgae are suspended in water, making them easily consumed by filter-feeding aquatic organisms, leading to population decline. Furthermore, suspended microalgae can cause secondary pollution when they enter natural water bodies. Secondly, autotrophic microalgae are less effective than bacteria at removing organic matter, and external environmental factors such as light significantly impact their nitrogen and phosphorus removal. This makes it difficult for microalgae alone to achieve satisfactory results in treating aquaculture wastewater. Algae-bacteria symbionts combine the advantages of both algae and bacteria in bioremediation, such as large surface area, ease of cultivation, and low propagation costs. In algae-bacteria symbiotic systems, the synergistic effect of microalgae and bacteria plays a significant role in removing pollutants from water. Microalgae can utilize CO2 released by bacteria as an important carbon source for their growth, while also providing bacteria with O2, inorganic nutrients, and various organic substances. This alleviates, to some extent, the inhibition of denitrification caused by insufficient carbon sources in aquaculture wastewater. Because the effluent quality of suspended algae-bacterial symbiotic systems is easily affected by suspended microalgae and bacteria, and separation and harvesting are difficult, with long hydraulic retention times and large sludge production, it is necessary to immobilize the algae and bacteria in practice. Common immobilization methods include encapsulation and biofilm methods. The biofilm method utilizes the ease with which bacteria and microalgae attach, immobilizing them on a packing carrier. It offers high pollutant removal efficiency and facilitates the recovery of biomass resources such as algae and bacteria. Biofilm-immobilized algae-bacterial symbiotic systems have broad application prospects in wastewater treatment; however, existing carriers are mainly inorganic packing materials such as zeolite, ceramsite, and activated carbon, or organic polymer materials such as polyurethane and polyvinyl chloride, resulting in high costs and hindering the widespread application of this technology in aquaculture wastewater treatment. Summary of the Invention

[0004] The purpose of this invention is to provide a straw-based biofilm carrier and its preparation method, using crop straw as the biofilm carrier to construct an algae-bacteria symbiotic system and apply it to the treatment of aquaculture wastewater. Straw serves as a carrier and filler for the growth of microalgae and bacteria; furthermore, during degradation, it slowly releases organic matter, which acts as a carbon source for the microorganisms attached to it. Microalgae photosynthesis provides oxygen for aerobic bacteria. This invention eliminates the need for aeration when treating aquaculture wastewater; the impact of water flow periodically peels off the aged biofilm on the filler and collects it as fish feed. Simultaneously, organic matter and nutrients such as nitrogen and phosphorus can be recovered and utilized in the treatment of aquaculture wastewater.

[0005] To achieve these objectives and other advantages according to the present invention, a method for preparing a straw-based biofilm carrier is provided, comprising the following steps:

[0006] S1. The straw is woven into a mesh-like fabric and then further processed, specifically:

[0007] S1.1 Spray a 0.5-1.0% sodium carboxymethyl cellulose solution evenly onto the surface of the straw woven fabric until it is moistened, then spray wheat flour evenly onto the surface of the straw woven fabric and let it dry for later use.

[0008] S1.2 Spray a 5% polyvinyl alcohol solution evenly onto the dried straw woven fabric surface. After the straw woven fabric is dry, spray a 3-5% CaCl2 solution evenly onto its surface. Then, spray a 5-10% sodium alginate solution evenly onto the straw woven fabric surface.

[0009] S1.3 When the straw woven fabric is half-dry and a transparent film forms on the surface, spray biochar powder evenly onto the surface of the straw woven fabric; after the surface of the straw woven fabric is dry, first spray a Fe(NO3)3 solution with a mass concentration of 2-3% onto the surface, then spray ammonia water with a mass concentration of 3-5%, and then let it air dry naturally.

[0010] S2. The denitrified flocculent sludge and fishpond bottom mud after acclimation of activated sludge are inoculated into a denitrification expander for expansion; after 5 days of expansion, the straw woven material treated in S1 is placed in the denitrification expander for 10 days of cultivation until a flocculent biofilm grows on the surface of the straw woven material, thus completing the bacterial biofilm formation.

[0011] S3. After the bacterial biofilm formation is completed, add microalgae solution and BG11 culture medium to the denitrification propagator and culture for 5-7 days. When the surface of the straw is covered with microalgae, the straw-based biofilm carrier is obtained.

[0012] The beneficial effects of adopting the above-mentioned further scheme are as follows: In this further scheme, rice straw, wheat straw, or reed stalks can be used. The treated straw woven fabric has good durability in water and can quickly form a biofilm. At the same time, the biochar contained therein can adsorb and enrich pollutants such as nitrogen and phosphorus in the water, thereby increasing the concentration of nutrients around the microbial living environment and thus removing pollutants more effectively. Spraying Fe(NO3)3 solution onto the surface of the straw woven fabric, iron ions have a promoting effect on algal growth, and the introduction of iron ions can accelerate the formation of algal biofilms.

[0013] Furthermore, in the method for preparing a straw-based biofilm carrier, the straw used in S1 undergoes pretreatment, specifically:

[0014] Add 0.5-1% quicklime and 0.2-0.5% sodium chloride to water and stir well. Then soak the cleaned straw in the solution for 24 hours. Remove the straw and let it dry. Then soak it in a 0.2-0.5% Na2SO3 solution for another 24 hours. Remove the straw and let it dry for later use.

[0015] The beneficial effects of adopting the above-mentioned further solution are: in this further solution, the pretreatment can not only increase the surface roughness of the straw, but also improve its mechanical properties and enhance its tensile strength.

[0016] Furthermore, in the method for preparing a straw-based biofilm carrier, the preparation method of the biochar powder used for spraying in S1.3 is as follows:

[0017] After crushing wheat or corn straw and passing it through a 100-mesh sieve, the straw is soaked in a 5% FeCl3 solution for 48 hours and then heated at 400-500℃ in the absence of air for 2 hours to obtain the biochar powder.

[0018] The beneficial effect of adopting the above-mentioned further scheme is that the biochar powder prepared in this further scheme has a positive charge on its surface, which has an electrostatic attraction effect on negatively charged microalgae, and can promote the formation of algal biofilm.

[0019] Furthermore, in the method for preparing a straw-based biofilm carrier, in step S2, denitrifying flocculent sludge acclimated from activated sludge and pond bottom mud are inoculated into a denitrification expander and expanded under the conditions of COD of 2000 mg / L, nitrate nitrogen of 200 mg / L, total phosphorus of 20 mg / L, dissolved oxygen concentration of 0.2-0.5 mg / L, pH of 6.5-7.5, and controlled culture temperature of 25-35℃.

[0020] The beneficial effects of adopting the above-mentioned further scheme are: In this further scheme, compared with inorganic fillers, the filler made of straw has better biocompatibility and is more conducive to the attachment and growth of microorganisms.

[0021] Furthermore, in the method for preparing a straw-based biofilm carrier, after adding microalgae liquid and BG11 culture medium to the denitrification expander in step S3, the culture is carried out under the conditions of light intensity of 2000-3000 Lux, temperature of 25-30℃, and light-dark ratio of 12 / 12.

[0022] The beneficial effects of adopting the above-mentioned further scheme are as follows: In this further scheme, the straw is pretreated, and a thin film of iron hydroxide is formed on its surface, which can slowly release iron ions, promoting the growth of microalgae. At the same time, positively charged biochar is introduced into the straw, and the surface of the straw is positively charged as a whole, which has electrostatic attraction to microalgae and can promote the formation of microalgal biofilm.

[0023] The present invention also provides a straw-based biofilm carrier, which is prepared by the above-described preparation method.

[0024] This invention also provides a method for treating aquaculture wastewater using the above-mentioned straw-based biofilm carrier, comprising the following steps:

[0025] Step 1: Use a rectangular pool with a depth of 2.0-4.0m as the tailwater treatment area, and set multiple anti-fouling curtains at intervals along its length to divide it into multiple strip areas with a width of 2.0m-3.0m so that the water flow in the tailwater treatment area is S-shaped. Set inlet and outlet at both ends of the water flow direction respectively.

[0026] Step 2: In the strip area, multiple straw-based biofilm carriers are set at intervals of 2.0-3.0m along the width direction of the tailwater treatment zone, and the straw-based biofilm carriers are immersed 5-10cm below the water surface;

[0027] Step 3: After sedimentation and filtration of the aquaculture wastewater in the fishpond, the wastewater is discharged from the inlet into the wastewater treatment area for treatment for 48-96 hours, and then the treated wastewater is returned to the fishpond.

[0028] The beneficial effects of adopting the above-mentioned further scheme are as follows: In this further scheme, straw not only serves as a carrier for algal and bacterial growth, but the cellulose, hemicellulose, and other polysaccharides it contains will also gradually decompose during the treatment process, serving as a slow-release carbon source for microbial growth and denitrification. Excellent denitrification can be achieved without the need for additional organic carbon sources during the treatment process. Microalgae provide oxygen for aerobic bacteria through photosynthesis, eliminating the need for aeration in the treatment system and significantly reducing energy consumption. The detached algal and bacterial biofilm is collected by water flow and processed into fish feed, realizing the recovery and utilization of nutrients such as nitrogen and phosphorus in the tailwater.

[0029] Furthermore, the method for treating aquaculture wastewater using a straw-based biofilm carrier further includes the following steps:

[0030] Step 4: Obtain the ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration in the effluent using an online water quality monitoring device installed at the outlet, and pre-set the compliance thresholds for ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration.

[0031] When the ammonia nitrogen concentration, total nitrogen concentration and total phosphorus concentration of the effluent are all lower than the corresponding compliance threshold, the treated effluent will be returned to the fishpond.

[0032] When at least one of the ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration in the effluent is not lower than the corresponding compliance threshold, the treated effluent is stopped from being sent back to the fishpond, and the treated effluent is sent to the inlet so that it can re-enter the effluent treatment area for further treatment.

[0033] Furthermore, the method for treating aquaculture wastewater using a straw-based biofilm carrier further includes the following steps:

[0034] Step 5: Every 30 days, discharge water from the tailwater treatment area to half the tank volume, and at the same time increase the inlet flow rate by 2-3 times. The water flow will impact and peel off the mature and aged straw-based biofilm carrier in the tailwater treatment area. The detached straw-based biofilm carrier is collected through the sewage pipes on both sides of the tailwater treatment tank, and then sterilized, dehydrated and dried before being used as fish feed.

[0035] The present invention also provides an aquaculture wastewater treatment system employing the above-described aquaculture wastewater treatment method, comprising:

[0036] The tailwater treatment tank is equipped with an inlet and an outlet;

[0037] Multiple anti-fouling curtains are spaced apart along the length of the tailwater treatment tank, dividing the interior of the tailwater treatment tank into multiple strip-shaped areas so that the water flow in the tailwater treatment tank is S-shaped. The inlet and outlet are located at opposite ends of the water flow direction.

[0038] Multiple straw-based biofilm carriers are provided at intervals along the width direction of the tailwater treatment tank within the strip-shaped area;

[0039] An online water quality monitoring device is installed inside the tailwater treatment tank and near the outlet.

[0040] A water outlet pipe, one end of which is connected to the water outlet, and a valve is provided on the water outlet pipe;

[0041] A drain pipe, the two ends of which are connected to the water inlet and the water outlet respectively;

[0042] A water pump is installed on the drain pipe;

[0043] The sewage pipe is installed inside the tailwater treatment tank.

[0044] The beneficial effects of this invention are:

[0045] This invention uses crop straw as a carrier for algae and microbial biofilm formation. The pre-treated straw surface becomes rough, enhancing durability and improving biofilm formation capabilities, while maintaining low material costs. The straw not only serves as a carrier for algae and microbial growth, but the cellulose, hemicellulose, and other polysaccharides it contains also gradually decompose during treatment, providing a slow-release carbon source for microbial growth and denitrification. Excellent denitrification is achieved without the need for external organic carbon sources. Microalgae provide oxygen to aerobic bacteria through photosynthesis, eliminating the need for aeration and significantly reducing energy consumption. The detached algae and microbial biofilm is collected by water flow and processed into fish feed, realizing the recovery and utilization of nutrients such as nitrogen and phosphorus in the wastewater. This invention effectively removes nitrogen and phosphorus pollutants from aquaculture wastewater, employs a simple process with low equipment requirements, and utilizes nutrients through algae and microbial recovery, resulting in significant social, economic, and environmental benefits.

[0046] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0047] Figure 1 This is a flowchart of the aquaculture wastewater treatment method described in this invention;

[0048] Figure 2 This is a schematic diagram of the aquaculture wastewater treatment system described in this invention;

[0049] Figure 3 This is a schematic diagram illustrating the changes in ammonia nitrogen concentration during the wastewater treatment process in an embodiment of the present invention.

[0050] Figure 4 This is a schematic diagram illustrating the change in total nitrogen concentration during the wastewater treatment process in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram illustrating the change in total phosphorus concentration during the wastewater treatment process in an embodiment of the present invention. Detailed Implementation

[0052] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0053] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0054] An embodiment of the present invention provides a method for preparing a straw-based biofilm carrier, comprising the following steps:

[0055] S1. The straw is woven into a mesh-like fabric and then further processed, specifically:

[0056] S1.1 Spray a 0.5-1.0% sodium carboxymethyl cellulose solution evenly onto the surface of the straw woven fabric until it is moistened, then spray wheat flour evenly onto the surface of the straw woven fabric and let it dry for later use.

[0057] S1.2 Spray a 5% polyvinyl alcohol solution evenly onto the dried straw woven fabric surface. After the straw woven fabric is dry, spray a 3-5% CaCl2 solution evenly onto its surface. Then, spray a 5-10% sodium alginate solution evenly onto the straw woven fabric surface.

[0058] S1.3 When the straw woven fabric is half-dry and a transparent film forms on the surface, spray biochar powder evenly onto the surface of the straw woven fabric; after the surface of the straw woven fabric is dry, first spray a Fe(NO3)3 solution with a mass concentration of 2-3% onto the surface, then spray ammonia water with a mass concentration of 3-5%, and then let it air dry naturally.

[0059] S2. Equal amounts of denitrifying flocculent sludge acclimated to activated sludge and fishpond bottom mud are mixed (calculated as equal amounts based on the dry weight of the sludge after drying, i.e., dry sludge and dry bottom mud are mixed at a mass ratio of 1:1) and then inoculated into a denitrification expander for expansion cultivation. The sludge mass (based on dry sludge) is 1% of the culture medium mass. After 5 days of expansion cultivation, the straw woven fabric treated in S1 is placed in the denitrification expander for cultivation for 10 days until a flocculent biofilm grows on the surface of the straw woven fabric, completing the bacterial biofilm formation. Specifically, in S2, the denitrifying flocculent sludge acclimated to activated sludge and fishpond bottom mud are inoculated into the denitrification expander and expanded under the following conditions: COD 2000 mg / L, nitrate nitrogen 200 mg / L, total phosphorus 20 mg / L, dissolved oxygen mass concentration 0.2-0.5 mg / L, pH 6.5-7.5, and the culture temperature controlled at 25-35℃.

[0060] S3. After bacterial biofilm formation is complete, microalgae solution and BG11 culture medium are added to the denitrification expander and cultured for 5-7 days until the straw surface is covered with microalgae, thus obtaining the straw-based biofilm carrier. Specifically, in S3, after adding microalgae solution and BG11 culture medium to the denitrification expander, the culture is carried out under conditions of 2000-3000 Lux light intensity, 25-30℃ temperature, and a light / dark ratio of 12 / 12.

[0061] The straw used in S1 has undergone pretreatment, specifically:

[0062] Add 0.5-1% quicklime and 0.2-0.5% sodium chloride to water and stir well. Then soak the cleaned straw in the solution for 24 hours. After removing the straw and drying it, soak it in a 0.2-0.5% Na2SO3 solution for another 24 hours. Remove the straw and dry it for later use.

[0063] The preparation method of the biochar powder used in S1.3 spraying is as follows:

[0064] After crushing wheat or corn straw and passing it through a 100-mesh sieve, the straw is soaked in a 5% FeCl3 solution for 48 hours and then heated at 400-500℃ in the absence of air for 2 hours to obtain the biochar powder.

[0065] An embodiment of the present invention also provides a straw-based biofilm carrier, which is prepared by the above-described preparation method.

[0066] An embodiment of the present invention also provides a method for treating aquaculture wastewater using the above-mentioned straw-based biofilm carrier, comprising the following steps:

[0067] Step 1: Use a rectangular pool with a depth of 2.0-4.0m as the tailwater treatment area, and set multiple anti-fouling curtains at intervals along its length to divide it into multiple strip areas with a width of 2.0m-3.0m so that the water flow in the tailwater treatment area is S-shaped. Set inlet and outlet at both ends of the water flow direction respectively.

[0068] Step 2: In the strip area, multiple straw-based biofilm carriers are set at intervals of 2.0-3.0m along the width direction of the tailwater treatment zone, and the straw-based biofilm carriers are immersed 5-10cm below the water surface;

[0069] Step 3: After sedimentation and filtration of the aquaculture wastewater in the fishpond, the wastewater is discharged from the inlet into the wastewater treatment area for treatment for 48-96 hours, and then the treated wastewater is returned to the fishpond.

[0070] Step 4: Obtain the ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration in the effluent using an online water quality monitoring device installed at the outlet, and pre-set the compliance thresholds for ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration.

[0071] When the ammonia nitrogen concentration, total nitrogen concentration and total phosphorus concentration of the effluent are all lower than the corresponding compliance threshold, the treated effluent will be returned to the fishpond.

[0072] When at least one of the ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration in the effluent is not lower than the corresponding compliance threshold, the treated effluent is stopped from being sent back to the fishpond, and the treated effluent is sent to the inlet so that it can re-enter the effluent treatment area for further treatment.

[0073] Step 5: Every 30 days, discharge water from the tailwater treatment area to half of the tank volume, and at the same time increase the inlet flow rate by 2-3 times. The water flow will impact and peel off the mature and aged biofilm in the tailwater treatment area. The detached biofilm will be collected through the sewage pipes on both sides of the tailwater treatment tank, and then sterilized, dehydrated and dried before being used as fish feed.

[0074] Step Six: Replace the straw-based biofilm carrier regularly. When the effluent quality gradually deteriorates, the straw-based biofilm carrier should be replaced. Use a gradual, batch-by-batch replacement method, replacing the old straw-based biofilm carrier with a new one at each interval. Once the biofilm has successfully formed on the new straw-based biofilm carrier, then gradually replace the adjacent straw-based biofilm carriers.

[0075] The present invention also provides an aquaculture wastewater treatment system employing the above-described aquaculture wastewater treatment method, such as... Figure 2 As shown, it includes:

[0076] The tailwater treatment tank 4 is equipped with an inlet and an outlet, and an inlet pipe 1 and an outlet pipe 7 are respectively connected to the inlet and the outlet.

[0077] Multiple anti-fouling curtains 3 are spaced apart along the length of the tailwater treatment tank 4, dividing the interior of the tailwater treatment tank 4 into multiple strip-shaped areas so that the water flow in the tailwater treatment tank 4 is S-shaped. The inlet and outlet are located at opposite ends of the water flow direction.

[0078] Multiple straw-based biofilm carriers 5 are provided at intervals along the width direction of the tailwater treatment tank 4 within the strip-shaped area;

[0079] The water quality online monitoring device 6 is installed inside the tailwater treatment tank 4 and near the outlet.

[0080] A water outlet pipe 7, one end of which is connected to the water outlet, and a valve 8 is provided on the water outlet pipe 7;

[0081] The drain pipe 10 has its two ends connected to the water inlet and the water outlet 7, respectively.

[0082] Water pump 9 is installed on the drain pipe 10;

[0083] Sewage pipe 2 is installed inside the tailwater treatment tank 4.

[0084] Embodiments of the present invention provide an application of an algae-bacteria symbiotic system in the treatment of aquaculture wastewater, such as... Figure 1 As shown, specifically, it includes the following steps:

[0085] 1. Straw pretreatment:

[0086] After cleaning the rice straw, soak it in water for 24 hours. Add 1% quicklime and 0.3% sodium chloride to the water and stir well. After the straw is soaked and dried, soak it in a 0.4% Na2SO3 solution for another 24 hours. Then take it out and dry it for later use.

[0087] 2. Weaving and processing of straw carriers:

[0088] Pretreated rice straw was woven into a mesh-like mat, 3.0m long, 1.5m wide, and 2.0cm thick. After weaving, the mat surface was evenly sprayed with 0.8% sodium carboxymethyl cellulose. While the surface was still damp, wheat flour was sprayed on top, and the mat was then dried. Next, a 5% polyvinyl alcohol solution was evenly sprayed onto the woven surface. After drying, a 4% CaCl2 solution was evenly sprayed on the surface, followed by an 8% sodium alginate solution. The mat was then placed indoors to dry until semi-dry. When a transparent film began to form on the surface, biochar powder was evenly sprayed onto it. After the surface was completely dry, a 3% Fe(NO3)3 solution was sprayed on top, followed by a 3% ammonia solution, and then the mat was allowed to air dry naturally.

[0089] The preparation method of biochar powder includes: crushing wheat straw and passing it through a 100-mesh sieve, impregnating it with 5% FeCl3 for 48 hours, and then heating it at 400℃ in the absence of air for 2 hours to obtain biochar.

[0090] 3. Bacterial culture and biofilm formation:

[0091] After the straw-based biofilm carrier is prepared, bacterial culture and biofilm formation are carried out. Equal amounts (by dry weight) of denitrified flocculent sludge acclimated from a wastewater treatment plant and fishpond bottom mud are inoculated into a denitrification expander at a ratio of 1% by mass. The main nutrient configuration of the denitrification expander is: COD 2000 mg / L, nitrate nitrogen 200 mg / L, and total phosphorus 20 mg / L. Dissolved oxygen concentration in the culture medium is maintained at 0.2-0.5 mg / L, pH between 6.5 and 7.5, and the culture temperature is controlled at 25-35℃ by mechanical stirring and regular water changes. After 5 days of expansion, treated straw woven material is placed in the expander, and the same culture conditions are maintained for another 10 days. Biofilm formation is complete when flocculent biofilm grows on the surface of the straw.

[0092] 4. Microalgae biofilm formation:

[0093] After bacterial biofilm formation, *Chlorella proteoglycans* solution was added to the expander, along with BG11 culture medium, in addition to the existing nutrients. The mixture was cultured for 7 days under conditions of 2000-3000 Lux light intensity, 25-30℃ temperature, and a light / dark ratio of 12 / 12. The straw surface became covered with microalgae, thus obtaining the algae-bacterial biofilm. This algae-bacterial biofilm symbiotic system was used to treat the wastewater from a bass farm. The wastewater treatment area was 22m long and 12m wide, divided into seven 3m × 11m strip areas by a fouling screen. Five algae-bacterial biofilm carriers were placed in each strip area. The farm wastewater, after sedimentation and filtration, entered the wastewater treatment area and remained for 72 hours before being discharged. The influent and effluent water quality of the farm wastewater are shown in the attached figure. Figure 3 -Appendix Figure 5As shown in the figure, the algae-bacteria symbiotic system effectively removes nitrogen and phosphorus from aquaculture effluent, with an average removal rate of 72.08% for ammonia nitrogen, 70.45% for total nitrogen, and 66.67% for total phosphorus. During the 420-day operation period, the nitrogen and phosphorus levels in the effluent did not exceed the set thresholds. However, after 385 days of continuous operation, the effluent quality declined, indicating that some of the straw-based biofilm carrier had decayed, reducing the efficiency of pollutant removal.

[0094] On day 421, the biofilm carrier was gradually replaced, using a method of replacing one carrier at a time. First, half of the biofilm carrier was replaced. After one month, the newly replaced biofilm carrier was fully covered with algae and bacteria biofilm, at which point the other half of the biofilm carrier was replaced. The influent and effluent water quality after biofilm carrier replacement is shown in the attached figure. Figure 3-5 As shown in the figure, it can be seen that the effluent quality of the tailwater treatment area gradually improved after the biofilm was replaced, and after three months of continued operation, it achieved the initial treatment effect.

[0095] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for preparing a straw-based biofilm carrier, characterized in that, Includes the following steps: S1. The straw is woven into a mesh-like fabric and then further processed, specifically: S1.1 Spray a 0.5-1.0% sodium carboxymethyl cellulose solution evenly onto the surface of the straw woven fabric until it is moistened, then spray wheat flour evenly onto the surface of the straw woven fabric and let it dry for later use. S1.2 Spray a 5% polyvinyl alcohol solution evenly onto the dried straw woven fabric surface. After the straw woven fabric is dry, spray a 3-5% CaCl2 solution evenly onto its surface. Then, spray a 5-10% sodium alginate solution evenly onto the straw woven fabric surface. S1.3 When the straw woven fabric is half-dry and a transparent film forms on the surface, spray biochar powder evenly onto the surface of the straw woven fabric; after the surface of the straw woven fabric is dry, first spray a Fe(NO3)3 solution with a mass concentration of 2-3% onto the surface, then spray ammonia water with a mass concentration of 3-5%, and then let it air dry naturally. S2. The denitrified flocculent sludge and fishpond bottom mud after acclimation of activated sludge are inoculated into a denitrification expander for expansion; after 5 days of expansion, the straw woven material treated in S1 is placed in the denitrification expander for 10 days of cultivation until a flocculent biofilm grows on the surface of the straw woven material, thus completing the bacterial biofilm formation. S3. After the bacterial biofilm formation is completed, add microalgae solution and BG11 culture medium to the denitrification propagator and culture for 5-7 days. When the surface of the straw is covered with microalgae, the straw-based biofilm carrier is obtained.

2. The method for preparing a straw-based biofilm carrier as described in claim 1, characterized in that, The straw used in S1 has undergone pretreatment, specifically: Add 0.5-1% quicklime and 0.2-0.5% sodium chloride to water and stir well. Then soak the cleaned straw in the solution for 24 hours. Remove the straw and let it dry. Then soak it in a 0.2-0.5% sodium sulfite solution for another 24 hours. Remove the straw and let it dry for later use.

3. The method for preparing a straw-based biofilm carrier as described in claim 1, characterized in that, The preparation method of the biochar powder used for spraying in S1.3 is as follows: After crushing wheat or corn straw and passing it through a 100-mesh sieve, the straw is soaked in a 5% FeCl3 solution for 48 hours and then heated at 400-500℃ in the absence of air for 2 hours to obtain the biochar powder.

4. The method for preparing a straw-based biofilm carrier as described in claim 1, characterized in that, In S2, denitrifying flocculent sludge acclimated with activated sludge and fishpond bottom mud are inoculated into a denitrification expander and expanded under the following conditions: COD 2000 mg / L, nitrate nitrogen 200 mg / L, total phosphorus 20 mg / L, dissolved oxygen concentration 0.2-0.5 mg / L, pH 6.5-7.5, and culture temperature controlled at 25-35℃.

5. The method for preparing a straw-based biofilm carrier as described in claim 1, characterized in that, After adding microalgae solution and BG11 culture medium to the denitrification propagator in S3, the plants are cultured under conditions of light intensity of 2000-3000 Lux, temperature of 25-30℃, and light / dark ratio of 12 / 12.

6. A straw-based biofilm carrier, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. A method for treating aquaculture wastewater using the straw-based biofilm carrier as described in claim 6, characterized in that, Includes the following steps: Step 1: Use a rectangular pool with a depth of 2.0-4.0m as the tailwater treatment area, and set multiple anti-fouling curtains at intervals along its length to divide it into multiple strip areas with a width of 2.0m-3.0m so that the water flow in the tailwater treatment area is S-shaped. Set inlet and outlet at both ends of the water flow direction respectively. Step 2: In the strip area, multiple straw-based biofilm carriers are set at intervals of 2.0-3.0m along the width direction of the tailwater treatment zone, and the straw-based biofilm carriers are immersed 5-10cm below the water surface; Step 3: After sedimentation and filtration of the aquaculture wastewater in the fishpond, the wastewater is discharged from the inlet into the wastewater treatment area for treatment for 48-96 hours, and then the treated wastewater is returned to the fishpond.

8. The method for treating aquaculture wastewater using a straw-based biofilm carrier as described in claim 7, characterized in that, It also includes the following steps: Step 4: Obtain the ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration in the effluent using an online water quality monitoring device installed at the outlet, and pre-set the compliance thresholds for ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration. When the ammonia nitrogen concentration, total nitrogen concentration and total phosphorus concentration of the effluent are all lower than the corresponding compliance threshold, the treated effluent will be returned to the fishpond. When at least one of the ammonia nitrogen concentration, total nitrogen concentration, and total phosphorus concentration in the effluent is not lower than the corresponding compliance threshold, the treated effluent is stopped from being sent back to the fishpond, and the treated effluent is sent to the inlet so that it can re-enter the effluent treatment area for further treatment.

9. The method for treating aquaculture wastewater using a straw-based biofilm carrier as described in claim 8, characterized in that, It also includes the following steps: Step 5: Every 30 days, discharge water from the tailwater treatment area to half the tank volume, and at the same time increase the inlet flow rate by 2-3 times. The water flow will impact and peel off the mature and aged straw-based biofilm carrier in the tailwater treatment area. The detached straw-based biofilm carrier is collected through the sewage pipes on both sides of the tailwater treatment tank, and then sterilized, dehydrated and dried before being used as fish feed.

10. An aquaculture wastewater treatment system employing the aquaculture wastewater treatment method according to any one of claims 7-9, characterized in that, include: The tailwater treatment tank is equipped with an inlet and an outlet; Multiple anti-fouling curtains are spaced apart along the length of the tailwater treatment tank, dividing the interior of the tailwater treatment tank into multiple strip-shaped areas so that the water flow in the tailwater treatment tank is S-shaped. The inlet and outlet are located at opposite ends of the water flow direction. Multiple straw-based biofilm carriers are provided at intervals along the width direction of the tailwater treatment tank within the strip-shaped area; An online water quality monitoring device is installed inside the tailwater treatment tank and near the outlet. A water outlet pipe, one end of which is connected to the water outlet, and a valve is provided on the water outlet pipe; A drain pipe, the two ends of which are connected to the water inlet and the water outlet respectively; A water pump is installed on the drain pipe; The sewage pipe is installed inside the tailwater treatment tank.

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