Method for inducing formation of algal-bacterial biofilm by filamentous cyanobacteria through optical fiber and application thereof

Abstract

The present application provides a method for inducing formation of algal-bacterial biofilm by filamentous cyanobacteria through optical fiber and application; the method for inducing formation of algal-bacterial biofilm by filamentous cyanobacteria through optical fiber comprises: selectively inducing filamentous cyanobacteria to adhere and grow on the surface of a tannin-functionalized optical fiber carrier to form algal-bacterial biofilm; the method can form a local, recoverable and directional screening engineering microenvironment on the surface of a side-emitting optical fiber carrier, so that selective enrichment of filamentous cyanobacteria is realized; after the stable algal-bacterial biofilm is formed on the surface of the tannin-functionalized optical fiber carrier, the application is suitable for purifying low-carbon-nitrogen-ratio water bodies such as aquaculture tail water and farmland drainage water.

Description

Technical Field

[0001] This invention relates to a method and application of inducing filamentous cyanobacteria to form algal biofilms via optical fibers, belonging to the fields of aquaculture wastewater treatment, aquatic environment bioremediation, and engineered cultivation of algal biofilms. Background Technology

[0002] Aquaculture wastewater typically has characteristics such as high suspended solids content, high turbidity, high nitrogen and phosphorus concentrations, and low carbon-to-nitrogen ratio. If discharged directly without effective treatment, it can easily lead to eutrophication, algal blooms, and ecological degradation of the receiving water body. Although existing methods such as ecological ponds, artificial wetlands, and natural sedimentation have low operating costs, they generally suffer from problems such as large land area requirements, long start-up periods, and unstable denitrification efficiency under low carbon-to-nitrogen ratio conditions.

[0003] Algal-bacterial biofilms are considered an important engineering technology direction for aquaculture wastewater treatment due to their advantages of combining algal photosynthetic absorption, bacterial degradation and transformation, easy biomass maintenance, and resistance to hydraulic disturbance.

[0004] The treatment efficiency of algal biofilms is highly dependent on the growth status, spatial structure, and light supply of the algal biofilm on the carrier surface. Light is a basic condition for photosynthetic microorganisms such as cyanobacteria and microalgae to maintain growth and transform pollutants. Only when light energy is stably transmitted to the carrier surface and the interior of the algal biofilm can photosynthetic microorganisms continuously absorb nutrients, release oxygen, and secrete extracellular organic matter, and further support the nitrification, denitrification, and organic matter degradation processes of bacteria.

[0005] However, the high turbidity and numerous suspended particles in aquaculture wastewater make it difficult for external light sources to penetrate the water evenly, resulting in insufficient light on the carrier surface, decreased photosynthetic activity of algae and bacteria biofilms, low algae and bacteria ratio, and slow biomass accumulation.

[0006] To address the problem of insufficient light, existing technologies utilize light-guiding materials to transmit light into the water body or within algal and bacterial biofilms, such as side-emitting optical fibers, light guide plates, and hollow optical fibers. Side-emitting optical fibers can conduct light axially and release it from the sidewall, mitigating light attenuation caused by water turbidity to some extent. However, in actual biofilm formation, using optical fibers alone as a carrier still has significant shortcomings: First, the surface of optical fibers is usually smooth, resulting in weak initial adhesion of algae and bacteria and a long biofilm formation period. Second, existing optical fiber carriers mainly improve light transmission conditions, making it difficult to selectively target early algal and bacterial communities, easily leading to the formation of loosely structured, disturbance-resistant ordinary algal and bacterial biofilms. Third, if mechanical roughening or permanent coating is used to improve the adhesion of the optical fiber surface, it may cause a long-term decrease in light transmittance, affecting the light utilization efficiency in the mature operation stage.

[0007] Filamentous cyanobacteria possess filamentous entanglement, spatial support, and the ability to secrete extracellular polysaccharides. They can serve as a dominant skeletal group in algal biofilms, forming a three-dimensional network structure on the carrier surface. This provides attachment sites for spherical cyanobacteria, heterotrophic bacteria, and denitrifying bacteria, and enhances the thickness, adhesion, and resistance to shedding of the algal biofilm. Especially in low C / N ratio wastewater, the extracellular polysaccharides secreted by filamentous cyanobacteria not only enhance the structural stability of the algal biofilm but also serve as a particulate or aggregated carbon source. After conversion by associated heterotrophic bacteria, these polysaccharides provide usable carbon sources for the denitrification process. Furthermore, they can further adsorb other microorganisms, combining with the secreted polysaccharides to form and increase the biomass of the algal biofilm, promoting biofilm stability, biomass recovery, and pollutant removal. Therefore, the targeted induction of filamentous cyanobacteria as the dominant skeletal species in real indigenous algal-bacterial systems is key to improving the stability of algal biofilm engineering applications.

[0008] Existing patent CN108152882B discloses a side-emitting optical fiber with spiral grooves and its preparation method. This method improves the side-emitting efficiency and surface roughness by setting spiral grooves on the surface of the optical fiber cladding. However, its core is physical structure modification, which makes it difficult to achieve targeted regulation of early community composition of algal biofilms, enrichment of filamentous cyanobacteria, and secretion of extracellular polysaccharides. Existing patent CN107193081B discloses a hollow optical fiber and its preparation method for enhancing microalgal cell adsorption and biofilm growth. This method mainly relies on multilayer composite structures to improve the transfer of light, heat, and nutrient substrates, but it cannot regulate the targeted formation of the filamentous cyanobacterial skeleton structure and the construction of algal-bacterial metabolic networks in the tailwater of low carbon-nitrogen ratio aquaculture.

[0009] Furthermore, simply adjusting the intensity of the external light source cannot simultaneously solve the problems of rapid biofilm formation, localized directional screening, and stable operation during the maturation stage. External dimming mainly alters the overall light environment of the reactor, but it cannot construct a chemical interface on the surface of the optical fiber carrier that is conducive to the initial anchoring of microorganisms, nor can it create localized selective pressure on the carrier surface that matches the enrichment of filamentous cyanobacteria. Therefore, there is an urgent need in this field for an engineered method that can simultaneously achieve light guidance inside the optical fiber, rapid attachment to the carrier surface, directional enrichment of filamentous cyanobacteria, light intensity recovery during the maturation stage, and efficient removal of pollutants. Summary of the Invention

[0010] This invention proposes a method and application for inducing filamentous cyanobacteria to form algal biofilms through optical fibers. Its purpose is to solve the problems of loose structure and weak initial adhesion in the process of forming algal biofilms on the surface of optical fiber carriers in the existing technology.

[0011] The technical solution of the present invention is a method for inducing filamentous cyanobacteria to form an algal biofilm by means of optical fiber. The method includes: selectively inducing filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier using a tannin-functionalized optical fiber carrier to form an algal biofilm.

[0012] Furthermore, the filamentous cyanobacteria include Desertifilum , Nodosilinea , Leptolyngbya , Phormidium One or more of them.

[0013] Furthermore, the method for preparing the tannin-functionalized optical fiber carrier includes: cleaning the side-emitting optical fiber and coating the surface of the side-emitting optical fiber with a tannin active coating to obtain the tannin-functionalized optical fiber carrier.

[0014] Furthermore, the tannin-active coating is formed by tannic acid and a film-forming aid; the film-forming aid includes one or a combination of several of polyvinyl alcohol, boric acid, gelatin, and sodium alginate.

[0015] Furthermore, the side-emitting optical fiber surface is coated with a tannin-active coating to obtain a tannin-functionalized optical fiber carrier, specifically including: Step A): First, prepare a mixed solution of polyvinyl alcohol / black thorn tannin, with a total mass fraction of 6%–12% for the mixed solutes, wherein the mass ratio of polyvinyl alcohol to black thorn tannin is 3:1–5:1. Then, heat the mixed solution at 80°C–98°C for 1–3 hours, and then cool it to room temperature. Next, under stirring, add the resulting mixed solution dropwise to a 1%–3% boric acid solution to form a mixture. Then, store the mixture in a refrigerator at 2°C–6°C for 4–7 hours to allow cross-linking, thereby obtaining tannin sol. Step B) Subsequently, the cleaned side-emitting optical fiber is immersed in tannin sol to coat the surface of the side-emitting optical fiber with a tannin active coating. Step C) The side-emitting optical fiber coated with tannin active coating is dried at 20 ℃~40 ℃ for 20 min~50 min; then cured at 60 ℃~90 ℃ for 20 min~50 min to obtain tannin functionalized optical fiber carrier.

[0016] Furthermore, the selective induction of filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier using tannin-functionalized optical fiber carrier to form an algal biofilm specifically includes: 1) Place the tannin-functionalized optical fiber carrier into an algal culture containing filamentous cyanobacteria or into the water body to be treated; 2) Connect one or both ends of the tannin-functionalized optical fiber carrier to the light source, start the light source to make the light conduct along the inside of the side-emitting optical fiber, and release it from the side of the side-emitting optical fiber to induce filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier to form an algal biofilm.

[0017] Furthermore, the activation of the light source causes light to propagate along the interior of the side-emitting optical fiber and releases light from the side of the optical fiber, inducing filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier, forming an algal biofilm. Specifically, this includes: 1-1) Selective attachment stage: The tannin-functionalized optical fiber carrier is placed in a reactor containing indigenous algal culture containing filamentous cyanobacteria. Every 12 to 48 hours, part of the culture medium containing suspended algae is discharged from the reactor liquid phase and an equal volume of water to be treated is added. The liquid phase replacement volume each time is 20% to 50% of the working volume of the reactor. 1-2) Film-forming enhancement stage: After the initial algae and bacteria attachment layer is formed on the surface of the tannin-functionalized optical fiber carrier, 80% to 100% of the water in the reactor is replaced every 18 to 36 hours.

[0018] Furthermore, the temperature of the algae-bacterial solution containing filamentous cyanobacteria or the water to be treated is controlled at 25±2 ℃, and the light source operates periodically with a light cycle of (8~16) hours of light / (8~14) hours of darkness.

[0019] Furthermore, the algae-bacterial solution containing filamentous cyanobacteria is an indigenous algae-bacterial system containing filamentous cyanobacteria from aquaculture ponds or aquaculture tailwater.

[0020] Furthermore, after a stable algal biofilm is formed on the surface of the tannin-functionalized optical fiber carrier, it is suitable for removing NH4 from nitrogen- and phosphorus-containing wastewater. + -N, NO3 - -N, NO2 - -N, COD, PO4 3- -P, TN, TP; when treating nitrogen and phosphorus-containing wastewater, the water temperature should be controlled at 20 ℃~35 ℃; the hydraulic retention time should be 12 hours~48 hours.

[0021] The beneficial effects of this invention are: 1) This invention does not simply use optical fiber to guide light, nor does it simply increase the roughness of the optical fiber surface. Instead, it constructs a time-responsive tannin active coating on the surface of the side-emitting optical fiber and combines it with internal illumination to form a local, recoverable, and directionally screenable engineered microenvironment on the surface of the side-emitting optical fiber carrier, thereby achieving selective enrichment of filamentous cyanobacteria. 2) The initial emitted light intensity of the unmodified optical fiber surface of this invention is controlled at 1500 lux to 1800 lux, and further reduced to 600 lux to 800 lux after tannin functionalization. During the selective attachment stage, the screening of filamentous cyanobacteria is enhanced. Subsequently, the light intensity is restored to 1000 lux to 1400 lux, so that the mature algal biofilm continues to be in a moderately low light state that is conducive to the maintenance of filamentous cyanobacteria, while avoiding continuous excessive light attenuation caused by permanent coating. 3) In this invention, the tannin active coating exerts a moderate allergic stress and extracellular polysaccharide induction effect; it induces filamentous cyanobacteria to secrete more extracellular polysaccharides, enabling filamentous cyanobacteria to form a three-dimensional skeleton on the optical fiber surface and enhance the attachment of other microorganisms; 4) This invention achieves a synergistic effect through the coupling of four elements: "internal light guiding in optical fiber, local low-light selection, tannin interface regulation, and time response recovery." The optical fiber solves the problem of insufficient light penetration in high-turbidity water; low light intensity provides a selective advantage for filamentous cyanobacteria; the tannin-active coating promotes initial attachment and induces extracellular polysaccharide secretion; and the coating's time response recovery prevents a decrease in light utilization efficiency during the mature stage. These technical features are not simply superimposed but work together to achieve the formation and stable maintenance of dominant species in the filamentous cyanobacteria framework. 5) This invention removes inefficiently attached microorganisms and air bubbles attached to the carrier surface through different stages of water exchange, thereby promoting the binding of filamentous cyanobacteria with the carrier. 6) This invention can achieve efficient pollutant removal in aquaculture wastewater with a low C / N ratio; in a preferred embodiment, the algal biofilm formed by the tannin-functionalized low-light-intensity optical fiber carrier effectively removes NH4+. + -N, NO3 - -N, COD, PO4 3 The removal rates of ⁻-P can reach 95.73%, 96.93%, 84%, and 89%, respectively, and the biomass of algae and bacteria biofilm is 2.37 times higher than that of optical fiber without tannin coating. 7) The technical effects of this invention are not only reflected in the improved endpoint removal rate, but also in the comprehensive improvement of biofilm formation speed, enrichment of filamentous cyanobacteria, secretion of extracellular polysaccharides, biomass of algae and bacteria biofilm (extracellular polymers composed of cyanobacteria, bacteria, polysaccharides, and proteins), density of algae and bacteria biofilm, and the coupling ability of algae and bacteria metabolism. Therefore, even if the endpoint removal rate of some pollutants is only slightly different from that of unmodified optical fiber, this invention still improves the system start-up efficiency and operational stability by significantly improving the structure and functional network of algae and bacteria biofilm. 8) The present invention uses widely available and low-cost materials such as tannic acid and polyvinyl alcohol (PVA) to prepare the coating. The process is simple and easy to scale up production and engineering installation. It is suitable for promotion and application in aquaculture wastewater treatment devices, recirculating aquaculture systems, ecological ditches, front-end reinforcement units of constructed wetlands and decentralized low-carbon wastewater treatment scenarios. Attached Figure Description

[0022] Figure 1 This is a physical image of the tannin-functionalized optical fiber carrier prepared according to the present invention.

[0023] Figure 2 This is a schematic diagram showing the position of the tannin-functionalized optical fiber carrier of the present invention in the reactor.

[0024] Figure 3This is a curve showing the change in emitted light intensity from the surface of the tannin-functionalized optical fiber carrier as a function of film attachment time in this invention.

[0025] Figure 4 These are microscopic images of the biofilm features on the optical fiber surface before and after the periodic partial liquid phase replacement during the selective attachment stage in this invention.

[0026] Figure 5 This is a diagram showing the formation of an initial algae and bacteria attachment layer on the surface of the tannin-functionalized optical fiber carrier in this invention, followed by the attachment of oxygen generated by photosynthesis to the optical fiber surface, the fiber rupture, and further coverage by the biofilm.

[0027] Figure 6 This is a scanning electron microscope image of the algal biofilm with filamentous cyanobacteria as its framework, formed in this invention.

[0028] Figure 7 This is a microscope image of indigenous filamentous cyanobacteria in the tailwater of actual aquaculture in this invention.

[0029] Figure 8 This is a comparison diagram of the coating effect on the surface of tannin-functionalized optical fiber carrier and unmodified optical fiber carrier in the embodiments.

[0030] Figure 9 This is a heatmap showing the abundance of the top 30 species in the filamentous cyanobacterial biofilm formed in the examples, and a comparison of the proportion of filamentous cyanobacteria.

[0031] Figure 10 This is a diagram showing the co-localization of cyanobacteria (red fluorescence) and polysaccharides (blue fluorescence) in the embodiment, as well as their spatial distribution (white fluorescence).

[0032] Figure 11 This is a comparison diagram of the pollutant removal effect when tannin-functionalized optical fiber carriers are used to treat aquaculture wastewater in the embodiments.

[0033] Figure 12 This is a comparison diagram of the biomass of algae and bacteria biofilms on tannin-functionalized optical fiber carriers and unmodified optical fiber carriers in the embodiments.

[0034] Figure 13 This is a comparison chart of the extracellular polysaccharide content of tannin-functionalized optical fiber carriers and unmodified optical fiber carriers in the embodiments. Detailed Implementation

[0035] A method for inducing filamentous cyanobacteria to form an algal biofilm using optical fibers, the method comprising: selectively inducing filamentous cyanobacteria to attach and grow on the surface of an optical fiber carrier using a tannin-functionalized optical fiber carrier to form an algal biofilm.

[0036] The filamentous cyanobacteria include Desertifilum (Tarsalsia salina) Nodosilinea (Arthrocystis), Leptolyngbya (Fine-sheathed filamentous algae) Phormidium One or more of the following (algae); preferably one or more of them. Desertifilum .

[0037] The method for preparing the tannin-functionalized optical fiber carrier includes: cleaning the side-emitting optical fiber and coating the surface of the side-emitting optical fiber with a tannin active coating to obtain the tannin-functionalized optical fiber carrier.

[0038] The cleaning process for the side-emitting optical fiber specifically includes cleaning the surface of the optical fiber sequentially with deionized water, ethanol, and acetone, or using a combination of deionized water, ethanol, and acetone to clean the surface of the optical fiber, in order to remove oil and impurities.

[0039] The tannin-active coating is formed by tannic acid and a film-forming aid; the film-forming aid includes one or a combination of several of polyvinyl alcohol, boric acid, gelatin, and sodium alginate, and the film-forming aid is further preferably polyvinyl alcohol and boric acid.

[0040] The process of coating the surface of the side-emitting optical fiber with a tannin-active coating to obtain a tannin-functionalized optical fiber carrier specifically includes the following steps: Step A) First, prepare a mixed solution of polyvinyl alcohol (PVA) / black tannin by mass fraction, wherein the total mass fraction of the mixed solute in the mixed solution is 6%–12%, and the mass ratio of PVA to black tannin is preferably 3:1–5:1, more preferably 4:1; then, heat the mixed solution at 80°C–98°C for 1–3 hours, and then cool it to room temperature; next, under stirring conditions, use a syringe to add the obtained mixed solution dropwise to a boric acid solution with a mass fraction of 1%–3% to form a mixture; then, place the mixture in a refrigerator at 2°C–6°C for 4–7 hours to allow it to crosslink, thereby obtaining tannin sol; the volume ratio of the boric acid solution to the mixed solution is preferably (0.5–1.5):5; more preferably, heat the mixed solution at 95°C for 2 hours, and then cool it to room temperature; next, under stirring conditions, use a 10 mL syringe to add the obtained solution dropwise to a boric acid solution with a mass fraction of 2% to form a mixture; then, place the mixture in a refrigerator at 4°C for 4 hours to form a mixture. The tannin sol is obtained by storing it in a °C refrigerator for 5 hours to allow it to cross-link, thereby obtaining the tannin sol; the volume ratio of the boric acid solution to the mixed solution is preferably 1:5. Step B): Subsequently, the cleaned side-emitting optical fiber is immersed in the tannin sol, and the tannin active coating is uniformly covered on the surface of the side-emitting optical fiber by immersion, rotation, lifting or repeated coating. Step C): The side-emitting optical fiber coated with the tannin active coating is dried at 20 ℃~40 ℃ for 20 min~50 min, preferably at 30 ℃ for 30 min; then cured at 60 ℃~90 ℃ for 20 min~50 min, preferably at 80 ℃ for 30 min, to obtain the tannin-functionalized optical fiber carrier. Figure 1 ).

[0041] The side-emitting optical fiber is selected as a side-emitting optical fiber capable of axially guiding light and emitting light from the sidewall; the diameter of the side-emitting optical fiber is preferably 1 mm to 5 mm, and more preferably 2 mm.

[0042] The side-emitting optical fiber can be configured as any of the following forms: straight, U-shaped, ring-shaped, spiral, bundled, or array-shaped. In application of this invention, it is preferable to bend the side-emitting optical fiber into a U-shape or bundled structure and fix both ends of the fiber to the light source connector. This facilitates uniform overall light emission from the side-emitting optical fiber. Then, the middle part of the side-emitting optical fiber is immersed in the water to be treated, which facilitates the construction of a treatment unit and scale-up applications. Figure 2 ).

[0043] The tannin-functionalized optical fiber carrier can be installed in any application location, such as reaction tanks, aquaculture wastewater treatment tanks, recirculating aquaculture wastewater treatment devices, ecological ditches, artificial wetland front-end reinforcement units, and modular wastewater treatment equipment.

[0044] The method of selectively inducing filamentous cyanobacteria to attach and grow on the surface of optical fiber carriers using tannin-functionalized optical fiber carriers to form an algal biofilm specifically includes the following steps: 1) Place the tannin-functionalized optical fiber carrier into an algal culture containing filamentous cyanobacteria or into the water to be treated; preferably, place a portion of the tannin-functionalized optical fiber carrier into a reactor containing an indigenous algal culture containing filamentous cyanobacteria. Figure 2 During operation, depending on the size of the reactor, a suitable hydrodynamic force is provided by a stirrer or water pump to ensure that the algae and bacteria are fully mixed in the water, with little or no sedimentation, so that the algae and bacteria can continuously contact the surface of the tannin-functionalized optical fiber carrier. 2) Connect one or both ends of the tannin-functionalized optical fiber carrier to the light source, start the light source, so that the light is transmitted along the inside of the side-emitting optical fiber and released from the side of the side-emitting optical fiber to induce filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier to form an algal biofilm; preferably, the two ends of the tannin-functionalized optical fiber carrier are connected to the light source, which is conducive to the uniform light emission of the entire optical fiber surface; in the early stage of the formation of algal biofilm, the tannin active coating on the surface of the tannin-functionalized optical fiber carrier plays two roles: (1) providing surface functional groups that are conducive to the attachment of algae and bacteria, and improving the initial film attachment ability of the optical fiber surface; (2) generating controllable shielding of the side-emitting light of the optical fiber, so that a local low light intensity environment of 600 lux to 800 lux is formed on the surface of the optical fiber ( Figure 3This facilitates the preferential attachment and growth of filamentous cyanobacteria on the carrier surface; preferably, the temperature of the algae-bacterial solution containing filamentous cyanobacteria or the water to be treated is controlled at 25±2 ℃, and the light source is preferably periodically operated, with the light cycle preferably being (8~16) hours of light / (8~14) hours of darkness.

[0045] The activation of the light source enables light to be conducted along the interior of the side-emitting optical fiber and released from the side of the optical fiber to induce filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier, forming an algal biofilm. This process specifically includes the following steps: 1-1) Selective attachment stage: Connect one or both ends of the tannin-functionalized optical fiber carrier to the light source, so that the light is conducted along the inside of the side-emitting optical fiber and released from the side of the optical fiber. During the selective attachment stage, the actual emitted light intensity on the surface of the tannin-functionalized optical fiber carrier is controlled to be 600 lux to 800 lux under illumination, so that a local low-light environment is formed on the carrier surface. Unlike biofilm formation methods that involve continuously exchanging water while the carrier is placed in an algae-bacterial solution, this invention performs periodic partial liquid-phase replacement on the biofilm formation system under low-light conditions: every 12 to 48 hours, preferably 24 hours, a portion of the culture medium containing suspended algae-bacteria is discharged from the reactor liquid phase, and an equal volume of water to be treated is added; the amount of liquid-phase replacement each time is preferably 20% to 50% of the reactor's working volume, more preferably 30% to 50%; Through periodic partial liquid-phase displacement, algae and bacteria with weaker binding to the carrier surface are pulled off by surface tension and moved out of the system with the water flow, while filamentous cyanobacteria that have formed attachments, filamentous entanglements, or extracellular matrix connections on the tannin-functionalized optical fiber surface are more likely to remain on the carrier surface. Figure 4 ); At the same time, periodically replenishing aquaculture wastewater allows the biofilm system to gradually transition from the pre-culture environment of algae and bacteria to the actual polluted water environment, avoiding the environmental mutation caused by directly exposing the initially attached algae and bacteria biofilm to the polluted water, thereby improving the stability of the algae and bacteria biofilm in subsequent treatment processes. As the operating time increases, the tannin active coating undergoes partial swelling, dissolution, or surface state changes, which weakens its shielding effect on the lateral emitted light of the optical fiber. Without changing the light source, the actual emitted light intensity on the optical fiber surface during illumination gradually recovers from 600 lux to 800 lux before coating to 1000 lux to 1400 lux. The selective adhesion stage lasts for 1 to 3 days, preferably 2 days. 1-2) Film-forming enhancement stage: During illumination, the emitted light intensity from the tannin-functionalized optical fiber carrier surface is maintained at 1000 lux to 1400 lux; after the initial algal-bacterial attachment layer forms on the surface of the tannin-functionalized optical fiber carrier, the oxygen produced by algal photosynthesis easily nucleates and forms attachment bubbles in the extracellular polymers of the algal-bacterial biofilm and the intercellular spaces of the algal-bacterial cells on the optical fiber surface. Figure 5 If the bubbles remain for a long time, they occupy the effective attachment sites on the fiber surface, blocking the contact between algal cells and the carrier surface, and exerting a local lifting and stretching effect on the algal biofilm. Therefore, the water above the lowest point of the fiber carrier in the reactor is replaced every 18 h to 36 h (preferably 24 h), usually 80% to 100% of the working volume of the reactor. During the replacement process, the liquid level in the reactor drops with the drainage process. The descending gas-liquid interface sweeps across the fiber surface in sequence, causing the oxygen bubbles that were originally surrounded by water and attached to the fiber surface to be concentrated and exposed to the air in a short time and connected to the outside air. The liquid film that maintains the bubble shape drains, thins and becomes unstable, which in turn causes the bubbles to break or directly merge into the gas phase. The fiber surface that was originally covered can be re-wetted by water and exposed as an attachment area. Figure 5 The surrounding algal and fungal cells can migrate, attach, and spread laterally in this area, increasing the coverage of the algal and fungal biofilm; the film-forming enhancement phase lasts for 5 to 15 days, preferably 11 days. In addition, by increasing the partial liquid phase replacement in the early stage of biofilm formation to a high proportion of liquid phase replacement, a second-stage hydraulic screening is applied to the initial algal biofilm that has already formed. Algae that are still in suspension and unstable in their binding with the carrier continue to be discharged from the system, while filamentous cyanobacteria and their associated microorganisms that have formed filamentous entanglements and extracellular matrix connections on the optical fiber surface are selectively retained. Under the aforementioned moderately low light conditions and continuous liquid-phase renewal, the filamentous cyanobacteria selectively retained on the carrier surface continue to proliferate and secrete extracellular polysaccharides. The filaments intertwine with each other and form a continuous three-dimensional network framework through the extracellular polysaccharides. The formed three-dimensional network framework further provides attachment space for spherical cyanobacteria, heterotrophic bacteria, and denitrifying bacteria, thereby contributing to the formation of an algal-bacterial biofilm with filamentous cyanobacteria as the framework. Figure 6 ); When the filamentous cyanobacterial biofilm on the surface of the tannin-functionalized optical fiber carrier forms a continuous covering structure and the biomass of the biofilm tends to stabilize, it enters the stabilization treatment stage.

[0046] During the stabilization phase, the light intensity emitted from the surface of the tannin-functionalized optical fiber carrier is maintained at 1000 lux to 1400 lux under illumination. The hydraulic residence time is set, preferably 24 hours. The water in the reactor is completely replaced with the water to be treated, and the formed filamentous cyanobacteria biofilm continuously removes pollutants.

[0047] During the stabilization process, the periodic water renewal can also continuously remove suspended algae and shed biomass newly entering the system, maintaining the algal biofilm structure with filamentous cyanobacteria as the framework.

[0048] When applying this invention, the indigenous algae-bacterial solution containing filamentous cyanobacteria is preferably an indigenous algae-bacterial system containing filamentous cyanobacteria from aquaculture ponds or aquaculture tailwater. Figure 7 This method does not require the addition of pure algae, has strong environmental adaptability, and is suitable for actual wastewater treatment scenarios. If not used for in-situ water treatment, indigenous algae-bacteria systems can be collected for pre-culture to form algae-bacteria solution. The pre-culture temperature is 20 ℃~30 ℃, preferably 25 ℃±2 ℃. When the chlorophyll a concentration in the algae-bacteria solution reaches 1 mg / L~8 mg / L, preferably 2 mg / L~5 mg / L, tannin-functionalized optical fiber carriers are placed in the algae-bacteria solution to induce filamentous cyanobacteria to attach and grow on the surface of the tannin-functionalized optical fiber carriers to form an algae-bacteria biofilm. After the algae-bacteria biofilm is formed on the surface of the tannin-functionalized optical fiber carriers, it is introduced into the polluted water body to be treated for treatment.

[0049] In this invention, low light intensity refers to the local emitted light intensity on the surface of the optical fiber carrier being within a low light intensity range suitable for the attachment and growth of filamentous cyanobacteria. Preferably, the initial emitted light intensity of the side-emitting optical fiber surface without the tannin active coating during illumination is 1500 lux to 1800 lux. After coating with the tannin active coating, the emitted light intensity on the optical fiber surface during the initial stage of biofilm formation during illumination decreases to 600 lux to 800 lux. After 1 to 5 days of biofilm formation, the tannin active coating undergoes partial swelling, dissolution, or microbial action in the water, and the emitted light intensity on the optical fiber surface recovers to 1000 lux to 1400 lux during illumination. Figure 3 Through the above settings, the tannin-functionalized optical fiber carrier forms a low light intensity in the early stage of biofilm formation, which is conducive to the screening and attachment of filamentous cyanobacteria; in the mature stage of algal biofilm, the light intensity gradually recovers to a moderately low light range, so as to maintain the dominance of filamentous cyanobacteria and avoid long-term excessive shading.

[0050] This invention, after forming a stable algal biofilm on the surface of a tannin-functionalized optical fiber carrier, is suitable for treating aquaculture wastewater or other low-carbon-to-nitrogen (C / N) nitrogen- and phosphorus-containing wastewater. During the treatment process, the side-emitting optical fiber continuously provides low internal light intensity (1000 lux to 1400 lux), maintaining the photosynthetic activity of filamentous cyanobacteria within the algal biofilm. The three-dimensional framework formed by the filamentous cyanobacteria enhances the stability of the algal biofilm. Extracellular polysaccharides enhance the adhesion of the algal biofilm and provide an interface for heterotrophic bacteria and denitrifying bacteria to attach and convert carbon sources. When treating aquaculture wastewater or other low-C / N nitrogen- and phosphorus-containing wastewater, the water temperature is controlled at 20°C to 35°C, preferably 25°C to 30°C; the hydraulic retention time is 12 h to 48 h, preferably 24 h; the illumination method is intermittent illumination, preferably 12 h of light / 12 h of darkness. This method can also be used to remove NH4. + -N, NO3 - -N, NO2 - -N, COD, PO4 3- -P, TN, TP and other pollutants, especially suitable for NH4 + -N, NO3 - -N synchronization removal.

[0051] Example 1

[0052] This embodiment provides a method for inducing filamentous cyanobacteria to form an algal biofilm using optical fibers. The specific process is as follows: A side-emitting optical fiber with a diameter of 2 mm was used as a carrier. It was cut to a length suitable for reactor installation and bent into a U-shape. The optical fiber was then cleaned with deionized water, ethanol, and acetone in sequence and dried for later use.

[0053] 40 g of PVA and 10 g of black thorn tannin were dissolved in 500 mL of deionized water. The mixture was then heated at 95 °C for 2 h and cooled to room temperature. Next, under stirring, the resulting solution was added dropwise to 100 mL of 2% boric acid solution using a 10 mL syringe to form a mixture. The mixture was then stored in a 4 °C refrigerator for 5 h to allow cross-linking, thereby obtaining tannin sol.

[0054] The cleaned optical fiber was immersed in the tannin sol, slowly rotated and pulled to evenly cover the surface of the optical fiber with the tannin sol; after repeating the immersion and pulling process 1 to 5 times, the coated optical fiber was dried at 30 ℃ for 30 min, and then cured at 80 ℃ for 30 min to obtain the tannin-functionalized optical fiber carrier. Figure 1 ).

[0055] The prepared tannin-functionalized optical fiber carrier was installed in a tailwater treatment reactor with an effective volume of 1.3 L, arranged as follows: Figure 2 As shown; the two ends of the optical fiber are connected to the light source, and the middle part is immersed in the algal solution containing filamentous blue-green algae; the reactor temperature is controlled at 25±2 ℃, the stirring speed is 300 rpm, and the photoperiod is 12 h light / 12 h dark.

[0056] During the selective attachment stage, the actual emitted light intensity on the surface of the tannin-functionalized fiber carrier under illumination was controlled to be 680 lux. Figure 3 Every 24 hours, 40% of the culture medium from the reactor's working volume is discharged, and an equal volume of culture medium with a concentration similar to that of aquaculture wastewater is added. During the liquid-phase replacement process, suspended algae and bacteria, as well as those weakly bound to the carrier, are discharged with the water flow, while algae that have already adhered to the surface and formed filamentous entanglements remain on the carrier surface. Simultaneously, the biofilm system gradually transitions from the pre-culture environment to the aquaculture wastewater environment. After two days of operation, a visible initial algae attachment layer forms on the surface of the tannin-functionalized optical fiber. Figure 4 Without changing the light source, the actual emitted light intensity on the fiber surface gradually recovers to 1360 lux under illumination. Figure 3 ).

[0057] The film-forming enhancement stage then begins, using aquaculture wastewater as the replacement fluid. Since the lowest point of the optical fiber carrier is extremely close to the bottom of the reactor, approximately one working volume of water is replaced every 24 hours. During drainage, the descending gas-liquid interface sequentially sweeps across the optical fiber surface, causing the photosynthetic oxygen-producing bubbles attached to the initial algal biofilm to rupture or merge into the gas phase. The area previously covered by these bubbles can be re-wetted by the water, providing space for the algae to continue attaching and spreading. Figure 5 After 13 days of continuous operation, the filamentous cyanobacteria intertwined to form a continuous three-dimensional network framework. Figure 6 A continuous blue-green algae biofilm forms on the surface of tannin-functionalized optical fibers. Figure 8 During this stage, as the biofilm thickens, the light intensity on the carrier surface decreases from 1360 lux to 1135 lux under illumination.

[0058] Subsequently, the process entered a stabilization phase. As the formation and shedding of the biofilm gradually reached equilibrium, the emitted light intensity from the optical fiber surface stabilized at approximately 1160 μX under illumination. Aquaculture wastewater was used as the water to be treated, and the hydraulic retention time was set to 24 hours. Stabilized algal biofilms were collected for metagenomic sequencing analysis. The results showed that the filamentous cyanobacteria in the algal biofilm on the tannin-functionalized optical fiber carrier mainly included… Desertifilum , Nostoc , Calothrix , Limnothrix and Oscillatoria ( Figure 9 ).

[0059] Laser confocal scanning microscopy (CLSM) was used to observe the spatial distribution of cyanobacteria (CLSM detects cyanobacteria, including filamentous and spherical cyanobacteria; however, the surface of the tannin-functionalized optical fiber carrier showed more filamentous cyanobacteria and extracellular polysaccharides spatially co-located, thus proving that the extracellular polysaccharides are mainly secreted by filamentous cyanobacteria; therefore, it is described below as: filamentous cyanobacteria and extracellular polysaccharides exhibit a clear spatial co-existence distribution) and extracellular polysaccharides in stable algal biofilms; Figure 10 As shown in the figure, the white area represents the overlap (co-localization) of the red fluorescence signal of cyanobacteria and the blue fluorescence signal of extracellular polysaccharides, indicating the consistency of spatial distribution. It can be seen from the figure that filamentous cyanobacteria and extracellular polysaccharides are clearly co-localized, indicating that extracellular polysaccharides are mainly secreted by filamentous cyanobacteria and distributed around filamentous cyanobacteria, which is beneficial to enhancing the adhesion and structural integrity of algal biofilms.

[0060] NH4 in simulated aquaculture wastewater + -N, NO3 - -N, COD, PO4 3- After treatment with -P, the removal rates reached 95.73%, 96.93%, 84%, and 89%, respectively, which are higher than the treatment efficiency of unmodified optical fiber carriers. Figure 11 ).

[0061] Comparative Example 1 The difference between this comparative example and Example 1 is that an unmodified optical fiber carrier is used, while the remaining process settings and operating conditions are the same as in Example 1.

[0062] After 14 days of operation, the surface of the unmodified optical fiber was observed; for example... Figure 8 As shown, the overall coverage of the algae and bacteria biofilm on the surface of the unmodified optical fiber carrier is lower than that in Example 1.

[0063] like Figure 9 As shown, the content of filamentous cyanobacteria in the algal biofilm on the surface of the tannin-functionalized optical fiber carrier is higher than that on the unmodified optical fiber carrier; in addition, the algal biofilm formed by the tannin-functionalized optical fiber carrier in Example 1 has a higher biomass ( Figure 12 ) and extracellular polysaccharide content ( Figure 13 The results indicate that while using side-emitting optical fibers with low light intensity can improve illumination conditions, it is insufficient to rapidly construct algal biofilms with filamentous cyanobacteria as the framework. The tannin-active coating plays a crucial role in initial attachment, enrichment of filamentous cyanobacteria, and enhancement of extracellular polysaccharides. The tannin-functionalized optical fiber carrier does not rely solely on optical fiber light guiding to improve algal growth, but rather constructs a stable algal biofilm suitable for engineering operation through the synergistic effect of "low light intensity optical fiber conduction - tannin interface attachment - filamentous cyanobacteria screening - extracellular polysaccharide enhancement".

Claims

1. A method for inducing filamentous cyanobacteria to form an algal biofilm using optical fibers, characterized by: include: Tannin-functionalized optical fiber carriers were used to selectively induce filamentous cyanobacteria to attach and grow on the surface of the optical fiber carriers, forming algal biofilms.

2. The method for inducing filamentous cyanobacteria to form an algal biofilm via optical fiber according to claim 1, characterized in that: The filamentous cyanobacteria include Desertifilum , Nodosilinea , Leptolyngbya , Phormidium One or more of them.

3. The method for inducing filamentous cyanobacteria to form an algal biofilm via optical fiber according to claim 1, characterized in that: The method for preparing the tannin-functionalized optical fiber carrier includes: cleaning the side-emitting optical fiber and coating the surface of the side-emitting optical fiber with a tannin active coating to obtain the tannin-functionalized optical fiber carrier.

4. The method for inducing filamentous cyanobacteria to form an algal biofilm using optical fibers according to claim 3, characterized in that: The tannin-active coating is formed by tannic acid and film-forming aids; the film-forming aids include one or a combination of several of polyvinyl alcohol, boric acid, gelatin, and sodium alginate.

5. The method for inducing filamentous cyanobacteria to form an algal biofilm via optical fiber according to claim 3, characterized in that: The side-emitting optical fiber is coated with a tannin-active coating to obtain a tannin-functionalized optical fiber carrier, specifically including: Step A): First, prepare a mixed solution of polyvinyl alcohol / black thorn tannin, with a total mass fraction of 6%–12% for the mixed solutes, wherein the mass ratio of polyvinyl alcohol to black thorn tannin is 3:1–5:

1. Then, heat the mixed solution at 80°C–98°C for 1–3 hours, and then cool it to room temperature. Next, under stirring, add the resulting mixed solution dropwise to a 1%–3% boric acid solution to form a mixture. Then, store the mixture in a refrigerator at 2°C–6°C for 4–7 hours to allow cross-linking, thereby obtaining tannin sol. Step B) Subsequently, the cleaned side-emitting optical fiber is immersed in tannin sol to coat the surface of the side-emitting optical fiber with a tannin active coating. Step C) The side-emitting optical fiber coated with tannin active coating is dried at 20 ℃~40 ℃ for 20 min~50 min; then cured at 60 ℃~90 ℃ for 20 min~50 min to obtain tannin functionalized optical fiber carrier.

6. A method for inducing filamentous cyanobacteria to form an algal biofilm via optical fiber according to any one of claims 1-5, characterized in that: The method of selectively inducing filamentous cyanobacteria to attach and grow on the surface of an optical fiber carrier using tannin-functionalized optical fiber carriers to form an algal biofilm specifically includes: 1) Place the tannin-functionalized optical fiber carrier into an algal culture containing filamentous cyanobacteria or into the water body to be treated; 2) Connect one or both ends of the tannin-functionalized optical fiber carrier to the light source, start the light source to make the light conduct along the inside of the side-emitting optical fiber, and release it from the side of the side-emitting optical fiber to induce filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier to form an algal biofilm.

7. The method for inducing filamentous cyanobacteria to form an algal biofilm via optical fiber according to claim 6, characterized in that: The activation of the light source causes light to be conducted along the interior of the side-emitting optical fiber and released from the side of the optical fiber to induce filamentous cyanobacteria to attach and grow on the surface of the optical fiber carrier, forming an algal biofilm. Specifically, this includes: 1-1) Selective attachment stage: The tannin-functionalized optical fiber carrier is placed in a reactor containing indigenous algal culture containing filamentous cyanobacteria. Every 12 to 48 hours, part of the culture medium containing suspended algae is discharged from the reactor liquid phase and an equal volume of water to be treated is added. The liquid phase replacement volume each time is 20% to 50% of the working volume of the reactor. 1-2) Film-forming enhancement stage: After the initial algae and bacteria attachment layer is formed on the surface of the tannin-functionalized optical fiber carrier, 80% to 100% of the water in the reactor is replaced every 18 to 36 hours.

8. A method for inducing filamentous cyanobacteria to form an algal biofilm using optical fibers according to claim 6, characterized in that: The temperature of the algae-bacterial solution containing filamentous cyanobacteria or the water to be treated is controlled at 25±2 ℃, and the light source operates periodically with a light cycle of (8~16) hours of light / (8~14) hours of darkness.

9. A method for inducing filamentous cyanobacteria to form an algal biofilm using optical fibers according to claim 6, characterized in that: The algae-bacterial solution containing filamentous cyanobacteria is an indigenous algae-bacterial system containing filamentous cyanobacteria from aquaculture ponds or aquaculture tailwater.

10. A method for inducing filamentous cyanobacteria to form an algal biofilm via optical fiber according to any one of claims 1-5, characterized in that... After a stable algal biofilm forms on the surface of tannin-functionalized optical fiber carriers, it is suitable for removing NH4 from nitrogen- and phosphorus-containing wastewater. + -N, NO3 - -N, NO2 - -N, COD, PO4 3- -P, TN, TP; when treating nitrogen and phosphorus-containing wastewater, the water temperature should be controlled at 20℃~35℃; the hydraulic retention time should be 12 hours~48 hours.

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