A bacteria-algae symbiotic constructed wetland system and a running method thereof

Abstract

This invention provides a fungal-algae symbiotic constructed wetland system and its operation method, relating to the field of rainwater treatment and resource utilization. The fungal-algae symbiotic constructed wetland system includes: a wetland bed, an inlet device, a drainage device, and a control unit. The system employs an upper and lower partitioned structure and alternating wet and dry operation, effectively improving its resistance to shock loads and significantly reducing system energy consumption by utilizing natural drainage and reoxygenation. The fungal-algae microspheres in the light-transmitting zone prevent bacterial loss, and the in-situ oxygen production by microalgae supports efficient denitrification by symbiotic bacteria. Combined with the synergistic retention effect of the bottom packing material in the non-light-transmitting zone, it ultimately achieves low-carbon and stable purification of multiple pollutants in complex runoff.

Description

Technical Field

[0001] This invention relates to the field of rainwater treatment and resource utilization, and more specifically, to a bacterial-algae symbiotic constructed wetland system and its operation method. Background Technology

[0002] Rainwater treatment and resource utilization are important ways to alleviate water shortages and control non-point source pollution. However, the pollutant composition of rainwater, especially initial rainwater and runoff, is usually quite complex, generally containing suspended particulate matter, organic matter, nitrogen and phosphorus nutrients, as well as some trace pollutants. It is characterized by a wide variety of pollutants, significant concentration fluctuations, and a low carbon-to-nitrogen ratio.

[0003] Currently, the main technologies for treating the aforementioned stormwater runoff include physicochemical methods and ecological methods. Physicochemical treatment methods typically involve sedimentation, filtration, or adsorption, and are relatively fast. Ecological treatment methods often employ traditional constructed wetlands, utilizing natural ecological processes for water purification. In addition, some treatment systems are also exploring the introduction of algae-bacterial symbiosis technology, utilizing the synergistic effect of algal oxygen production and microbial degradation of organic matter to treat specific types of wastewater.

[0004] While existing treatment technologies have played a role in water purification to some extent, they still exhibit certain limitations in practical applications. For example, physicochemical methods have relatively high operating costs and are prone to producing chemical sludge; traditional constructed wetlands often suffer from insufficient passive reoxygenation capacity, and the low dissolved oxygen concentration makes it difficult to meet the continuous metabolic needs of aerobic microorganisms, thus affecting denitrification efficiency. Furthermore, conventional algal-microbe symbiotic technologies often employ suspended growth or ordinary biofilms, which not only allow functional microbial communities to be easily lost with water flow but also have limited shock-absorbing capacity when facing the hydraulic impact of intermittent rainwater runoff with sudden increases in volume, easily leading to an imbalance in the system's symbiotic relationship and a sharp drop in treatment efficiency.

[0005] In summary, existing ecological treatment systems generally face technical bottlenecks when dealing with complex water quality and intermittent hydraulic shocks, including limited oxygen supply capacity, poor system microbial stability, and difficulty in simultaneously removing multiple pollutants. How to effectively buffer instantaneous fluctuations in hydraulic and pollution loads within a single treatment unit while maintaining the long-term survival of functional microorganisms and providing a stable aerobic environment is a pressing technical challenge that needs to be overcome in this field.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a bacterial-algae symbiotic constructed wetland system and its operation method. The system achieves efficient removal of multiple pollutants in complex runoff and strong shock buffering without external aeration by synergistic effects of in-situ oxygen production and denitrification by bacterial-algae microspheres and alternating dry and wet operation in upper and lower zones.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a fungal-algae symbiotic artificial wetland system, comprising: a wetland bed, a water inlet device, a drainage device, and a control unit; The wetland bed is divided into a light-transmitting zone and a non-light-transmitting zone at least from top to bottom along the water flow direction; the light-transmitting zone is filled with bacterial and algal microspheres; the bacterial and algal microspheres are co-embedded bodies containing heterotrophic nitrifying-aerobic denitrifying bacteria and microalgae; the non-light-transmitting zone is filled with packing material. The water inlet device is located at the upper part of the wetland bed and is used to introduce water to be treated into the light-transmitting area; The drainage device is located at the lower part of the wetland bed and is used to drain the treated water and empty the water inside the wetland bed. The control unit is connected to the water inlet device and the drainage device respectively, and is used to control the start and stop of water inlet and drainage so that the wetland bed can operate alternately periodically between the flooding period and the drying period.

[0009] In an optional embodiment, the wetland bed is divided into a water replenishment layer, a light-transmitting zone, a non-light-transmitting zone, and a support layer from top to bottom along the water flow direction.

[0010] In an optional embodiment, the outlet of the water inlet device is located above the water replenishment layer and is configured to introduce the water to be treated in a cascading manner; the control unit is configured to control the water replenishment layer to maintain a submerged water depth during the flooding period.

[0011] In an optional embodiment, the height of the light-transmitting area is 10cm to 30cm; and / or, The height of the non-transparent area is 30cm~50cm; and / or, The filler in the non-transparent area comprises large-particle-size filler with a particle size of 8mm to 15mm and small-particle-size filler with a particle size of 4mm to 6mm, which are graded and filled; and / or, The height of the supporting layer is 10cm to 20cm; and / or, The support layer is filled with support filler with a particle size of 20mm to 40mm.

[0012] In an optional embodiment, the filler in the opaque area is selected from at least one of zeolite, ceramsite, and limestone; and / or, The supporting filler in the support layer is pebbles and / or crushed stone.

[0013] In an optional embodiment, the particle size of the algal microspheres is 2 mm to 4 mm; and / or, The heterotrophic nitrifying-aerobic denitrifying bacteria include *Pseudomonas schistosomiasis*; and / or... The microalgae are selected from one or more combinations of Chlorella, Scenedesmus, Chlamydomonas, and Nostoc; and / or, The encapsulation matrix of the algal microspheres includes a cross-linked network of polyvinyl alcohol and boric acid, and sodium alginate; and / or, The microspheres contain a microscale dissolved oxygen gradient, with a dissolved oxygen concentration of 1.5 mg / L to 3.0 mg / L near the surface and decreasing to 0.2 mg / L to 0.8 mg / L towards the center; and / or, The control unit controls a wet-dry alternation cycle including controlling the flooding period to be 2h~6h and the drying period to be 4h~12h.

[0014] Secondly, the present invention provides a method for preparing microspheres of bacteria and algae, used to prepare microspheres of bacteria and algae in a symbiotic constructed wetland system as described in any of the foregoing embodiments, the method comprising: The activated heterotrophic nitrifying-aerobic denitrifying bacteria solution was mixed with the microalgae solution to obtain a bacterial-algae mixture. The bacterial-algae mixture was mixed with a solution containing polyvinyl alcohol and sodium alginate to prepare an encapsulation precursor solution. The embedding precursor solution was dropped into a crosslinking solution containing boric acid, and crosslinking and curing were performed to obtain microspheres. The formed microspheres were activated and cultured, and the light intensity was gradually reduced in the later stage of activation to acclimate them to weak light.

[0015] In an optional embodiment, the solution containing polyvinyl alcohol and sodium alginate has a polyvinyl alcohol mass fraction of 8%~10% and a sodium alginate mass fraction of 0.5%~1%; and / or, In the bacterial-algae mixture, the volume ratio of the activated heterotrophic nitrifying-aerobic denitrifying bacteria solution to the microalgae solution is 2:1; and / or, The pH of the crosslinking solution containing boric acid is 6.5-7.0; and / or, The step of dripping the embedding precursor solution into the crosslinking solution containing boric acid specifically includes: dripping the embedding precursor solution into the crosslinking solution at a dripping rate of 1 mL / min to 2 mL / min and a dripping height of 10 cm to 20 cm.

[0016] Thirdly, the present invention provides an operation method for controlling stormwater runoff pollution, employing a bacterial-algae symbiotic constructed wetland system as described in any of the foregoing embodiments, wherein the operation method includes at least one periodically alternating flooding step and a desiccation step: Flooding Steps: The water inlet device is turned on to introduce the rainwater runoff to be treated into the wetland bed in a cascading manner, and the wetland bed is kept submerged during the preset flooding period; wherein, the rainwater runoff flows sequentially through the light-transmitting area and the non-light-transmitting area, so as to use the light and the oxygen introduced by the cascading method to drive the bacteria and algae microspheres to carry out nitrogen and phosphorus removal reactions. Drying process: After the flooding period ends, the water inlet device is controlled to stop water intake, and the drainage device is controlled to drain the water inside the wetland bed. During the preset drying period, the wetland bed is kept in an empty state so that outside air can enter the wetland bed for atmospheric reoxygenation.

[0017] In an optional implementation, the flooding period lasts from 2 to 6 hours; and / or, The drying period is 4 to 12 hours.

[0018] Compared with existing technologies, the system provided by this invention utilizes a layered wetland bed combined with periodic operation of alternating wet and dry periods. This adapts to the intermittent and fluctuating characteristics of rainwater runoff, significantly improving its buffering and shock resistance to hydraulic and pollution load fluctuations. During the drying period, the system drains the water, allowing outside air to naturally enter the bed for atmospheric reoxygenation. This effectively restores the activity of aerobic microorganisms, overcoming the shortcomings of traditional wetlands' insufficient passive reoxygenation capacity, and eliminating the need for energy-intensive external aeration equipment.

[0019] The translucent zone is filled with co-embedded microspheres containing heterotrophic nitrifying-aerobic denitrifying bacteria and microalgae, effectively avoiding the bacterial population loss and imbalance problems that easily occur in traditional suspended growth or conventional biofilm forms, ensuring the long-term stability of the treatment system. Simultaneously, the microalgae receive light in the translucent zone and perform photosynthetic oxygen production, directly providing the dissolved oxygen needed for the metabolism of the co-embedded bacteria. This single microenvironment can meet the oxygen requirements for simultaneous nitrogen removal, significantly improving the nitrogen removal efficiency in complex water bodies with low C / N ratios.

[0020] The packing material installed in the non-transparent zone not only provides a good water flow channel, but also effectively receives and attaches shed biofilm and metabolic products migrating from the transparent zone above. This spatial partitioning design, with light-promoted denitrification in the upper part and interception and attachment in the lower part, combined with periodic water start-stop control, effectively improves the technical challenge of simultaneously removing multiple pollutants such as suspended solids, organic matter, nitrogen, and phosphorus from complex rainwater. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of one embodiment of the bacterial-algae symbiotic constructed wetland system in this application. Figure 2 This is a schematic flowchart of the preparation method of the bacterial and algal microspheres in the embodiments of this application.

[0023] Figure label: 100-Algae-bacterial symbiotic constructed wetland system; 1-Wetland bed; 11-Water replenishment layer; 12-Light-transmitting area; 13-Non-light-transmitting area; 14-Supporting layer; 2-Water inlet device; 3-Drainage device; 4-Control unit. Detailed Implementation

[0024] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0025] This application provides a bacterial-algae symbiotic constructed wetland system, which is mainly used to solve problems such as limited oxygen supply, easy loss of microorganisms, and insufficient shock resistance in existing ecological water treatment systems.

[0026] The system includes a wetland bed, a water inlet device, a drainage device, and a control unit. For example, in one embodiment, a schematic diagram may be shown... Figure 1 As shown.

[0027] The wetland bed is divided into a light-transmitting zone and a non-light-transmitting zone at least from top to bottom along the water flow direction; the light-transmitting zone is filled with bacterial and algal microspheres; the bacterial and algal microspheres are co-embedded bodies containing heterotrophic nitrifying-aerobic denitrifying bacteria and microalgae; the non-light-transmitting zone is filled with packing material.

[0028] The water inlet device is located on the upper part of the wetland bed and is used to introduce water to be treated into the light-transmitting area.

[0029] The drainage device is located at the bottom of the wetland bed and is used to drain the treated water and empty the water inside the wetland bed.

[0030] The control unit is connected to the water inlet device and the drainage device respectively, and is used to control the start and stop of water inlet and drainage so that the wetland bed can operate alternately periodically between the flooding period and the drying period.

[0031] The aforementioned wetland bed serves as the physical carrier for wastewater treatment, and its internal space is divided into at least two zones from top to bottom along the water flow direction: a light-transmitting zone and a non-light-transmitting zone. The light-transmitting zone is located at the upper part of the wetland bed, allowing it to receive natural or artificial light. This zone is filled with a large number of microbial and bacterial microspheres. These microspheres are co-embedded bodies made by mixing heterotrophic nitrifying-aerobic denitrifying bacteria with microalgae. In actual operation, the microalgae utilize light to perform photosynthesis and produce oxygen in situ, providing sufficient local dissolved oxygen for the bacteria encased within the same microspheres. This achieves efficient simultaneous nitrification and denitrification processes, and the encapsulation structure effectively prevents the loss of bacterial communities due to hydraulic erosion.

[0032] The non-transparent zone is located below the transparent zone, and physical packing material is disposed in this area. The packing material provides an excellent attachment matrix for biofilms and various metabolites that migrate or detach in the transparent zone above, further enhancing the system's retention and degradation capabilities.

[0033] To ensure stable operation of the above structure, the water inlet device is located at the upper part of the wetland bed, typically a water distribution pipe or an inlet valve, for introducing water to be treated into the light-transmitting area. The drainage device is located at the lower part of the wetland bed, typically a bottom perforated pipe or a drain valve, for discharging the treated clean water and for completely emptying the water from the inside of the wetland bed. The control unit is communicatively or electrically connected to both the water inlet device and the drainage device.

[0034] The control unit can be, for example, a programmable logic controller (PLC) or a timer relay. Through commands issued by the control unit, the system can automatically control the start and stop of the water inlet and drainage devices, allowing the wetland bed to operate cyclically between flooding and drying periods. During flooding, the system accumulates wastewater to ensure sufficient contact with the algae microspheres; during drying, the system drains the water, allowing external atmosphere to naturally infiltrate the bed for oxygenation. This low-cost restoration of aerobic microbial activity significantly improves the overall treatment efficiency and resistance to hydraulic shock.

[0035] In summary, the system provided in this embodiment, through its top-down spatial layout of translucent and non-translucent zones combined with alternating wet and dry cycles, significantly enhances its resilience to hydraulic and pollution fluctuations. Furthermore, it utilizes the drying period for energy-free natural atmospheric reoxygenation. The microspheres embedded with bacteria and algae within the translucent zone effectively prevent the loss of functional bacteria, directly supplying heterotrophic nitrification-aerobic denitrification bacteria with in-situ oxygen production from microalgae, achieving efficient simultaneous nitrogen removal without mechanical aeration. The packing material in the lower non-translucent zone further provides attachment space for metabolites migrating from the upper layer. The synergistic cooperation of all components significantly alleviates the problem of limited oxygen supply within a single system, achieving stable and efficient removal of multiple pollutants in complex water bodies.

[0036] In some embodiments, the wetland bed is divided into a water replenishment layer, a light-transmitting zone, a non-light-transmitting zone, and a support layer from top to bottom along the water flow direction.

[0037] This vertical, multi-layered spatial layout constructs a complete hydraulic buffer and biochemical reaction channel for the system. The uppermost water replenishment layer receives the introduced water to be treated and possesses excellent hydraulic energy dissipation and water uniformity, effectively buffering the physical impact of sudden large-volume rainwater runoff on the internal biochemical reaction media, allowing the water flow to be distributed smoothly and evenly downwards. Below the water replenishment layer, the light-transmitting zone and the non-light-transmitting zone are sequentially arranged, serving as the core nitrogen and phosphorus removal and interception degradation area of ​​the treatment system.

[0038] The support layer is located beneath the opaque area and is laid at the bottom of the wetland bed. On one hand, the support layer provides a stable physical support interface for the physical filler and algae microspheres filling above, preventing the internal media from migrating downwards with the water flow or causing pipe leakage. On the other hand, the support layer has a rich, large pore structure, which serves as a water collection buffer during flooding to ensure smooth drainage, and after the water has drained during the drying period, it acts as a bottom-level ventilation channel for the infiltration and diffusion of fresh air into the system. This support layer, in conjunction with the system's drainage operation, forms a three-dimensional air convection network, thereby significantly improving the efficiency of natural atmospheric reoxygenation and the system's long-term anti-clogging capability.

[0039] In some embodiments of this application, the hydraulic introduction structure of the system and the water level control method during operation have been further optimized.

[0040] Specifically, the outlet of the water inlet device is located above the water replenishment layer and is configured to introduce the water to be treated in a cascading manner; the control unit is configured to control the water replenishment layer to maintain a submerged water depth during the flooding period.

[0041] By employing a cascading water flow, the water being treated is allowed to freely fall and penetrate the air layer, resulting in a significant expansion of the gas-liquid contact surface. This facilitates the natural dissolution of fresh atmospheric oxygen into the water. This structural arrangement enables natural and efficient oxygenation of the water body without the need for additional high-energy-consuming mechanical aeration equipment, providing the necessary initial dissolved oxygen support for the subsequent metabolic activities of aerobic microorganisms within the system.

[0042] To ensure the stable operation of the cascading structure, the control unit is configured to maintain a submerged depth in the replenishment layer during the flooding period. In actual operation, the control unit can dynamically adjust the inflow and outflow water volume in conjunction with the liquid level monitoring equipment, allowing a surface buffer water layer of a certain thickness to accumulate within the replenishment layer area. This submerged water layer not only promotes the uniform distribution of the water to be treated across the horizontal cross-section of the wetland bed, but more importantly, it provides a flexible hydraulic buffer for the cascading water falling from above. The gravitational impact kinetic energy carried by the cascading water is largely dissipated by this water layer, transforming it into a gentle infiltration flow. This effectively prevents the high-speed water flow from directly scouring the reaction media in the light-transmitting and non-light-transmitting areas below, ensuring the structural integrity and long-term operational stability of the internal core nitrogen and phosphorus removal unit.

[0043] In some preferred embodiments of this application, the height distribution of each functional area within the system and the physical gradation of the filler have been further optimized, and specific features can be implemented individually or in combination.

[0044] In some embodiments, the height of the light-transmitting zone is 10cm to 30cm. For example, it can be 10cm, 12cm, 15cm, 18cm, 20cm, 22cm, 25cm, 28cm, 30cm, etc. Within this height range, external natural light can effectively penetrate the water and internal medium, ensuring that the microspheres of bacteria and algae located in the lower part of the light-transmitting zone can still receive sufficient light radiation, thereby maintaining the efficient photosynthetic oxygen production activity of the microalgae and avoiding the formation of light-transmitting dead zones at the bottom due to excessive depth.

[0045] In some embodiments, the height of the non-transparent zone is 30cm to 50cm. For example, it can be 30cm, 32cm, 35cm, 38cm, 40cm, 42cm, 45cm, 48cm, 50cm, etc. This thickness setting can provide a suitable hydraulic retention time for rainwater runoff, ensuring smooth water infiltration while allowing pollutants to be fully intercepted and biochemically degraded.

[0046] In some embodiments, the filler in the non-transparent area includes large-particle-size filler with a particle size of 8mm to 15mm (e.g., 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, etc.) and small-particle-size filler with a particle size of 4mm to 6mm (e.g., 4.0mm, 4.2mm, 4.5mm, 4.8mm, 5.0mm, 5.2mm, 5.5mm, 5.8mm, 6.0mm, etc.), and the two are graded and filled.

[0047] In actual operation, the large-diameter packing particles support each other to form a stable, highly porous framework, maintaining good water and air circulation channels; while the small-diameter packing particles are dispersed in the gaps between the framework, greatly enriching the specific surface area of ​​the system. This graded structure not only provides ample space for the attachment of detached biofilm and metabolic products, but also effectively reduces the risk of clogging caused by biomass accumulation during long-term operation of the system.

[0048] In some embodiments, the height of the support layer is 10cm to 20cm. For example, it can be 10cm, 11cm, 12cm, 14cm, 15cm, 16cm, 18cm, 19cm, 20cm, etc.

[0049] In some embodiments, the support layer is filled with support filler with a particle size of 20mm to 40mm. For example, it can be 20mm, 22mm, 25mm, 28mm, 30mm, 32mm, 35mm, 38mm, 40mm, etc.

[0050] Using larger particle size support packing not only reliably supports the graded packing and reaction medium above, preventing the loss of fine particles and blockage of the drainage pipes, but also the large pore structure it forms can quickly drain internal moisture and form unobstructed bottom ventilation chambers when the system enters the drying period. This facilitates the diffusion of fresh air from the outside into the wetland bed from bottom to top, thereby significantly enhancing the atmospheric reoxygenation performance of the system.

[0051] In some preferred embodiments of this application, in order to further enhance the system's simultaneous removal efficiency and operational stability of multiple pollutants, the filler materials selected for each functional area have been specifically configured.

[0052] Specifically, in some embodiments, the filler in the non-transparent area is selected from at least one of zeolite, ceramsite, and limestone.

[0053] In practical applications, depending on the specific characteristics of the water to be treated, one type of filler can be used alone, or two or three types can be mixed in a certain volume ratio for filling. When using expanded clay as filler, its rough surface and well-developed micropores provide an excellent carrier for the large-scale attachment of microorganisms and the rapid maturation of biofilms, thereby enhancing the degradation of organic matter. When using zeolite as filler, its unique cation exchange channels can effectively adsorb fluctuating ammonia nitrogen in the water, playing a significant buffering role against instantaneous high-concentration ammonia nitrogen shocks and providing a stable substrate supply for subsequent biological nitrification. When using limestone as filler, it can slowly release alkalinity under the erosion of water flow, which helps neutralize the acidic substances produced by the nitrification reaction to maintain a suitable pH environment in the system. At the same time, the calcium ions released by limestone easily react with phosphate ions in the water to form insoluble substances such as hydroxyapatite (HAP). In addition, the local increase in pH of the system can also induce trace amounts of magnesium and copper ions in the water to form magnesium phosphate, copper phosphate, and other precipitates, thereby synergistically improving the system's total phosphorus removal rate. The use or combination of any of these three fillers enhances the comprehensive purification capabilities of the non-transparent area from multiple dimensions, including physical adsorption, chemical precipitation, and biocompatibility.

[0054] In some embodiments, the support filler within the support layer is pebbles and / or crushed stone.

[0055] Pebbles and gravel possess extremely high mechanical compressive strength and excellent chemical stability. Laying these materials at the bottom of wetland beds not only allows them to withstand the long-term gravitational pressure of the water and various treatment media above without pulverizing or structural collapse, providing solid physical support for the entire reaction system; simultaneously, the highly stable, large-pore network formed by their accumulation ensures the continuous unobstructed flow of bottom drainage and ventilation channels, effectively avoiding the risk of system bottom blockage caused by the deposition of fine particles, and guaranteeing the reliable execution of wet-dry alternating operation cycles.

[0056] In some preferred embodiments of this application, the physicochemical parameters and biological composition of the core purification medium of the system, as well as the macroscopic operating cycle of the system, have been further optimized. The following features can be implemented individually or in combination to obtain better synergistic purification effects.

[0057] Specifically, in some embodiments, the particle size of the algal microspheres is 2mm to 4mm. For example, it can be 2.0mm, 2.2mm, 2.5mm, 2.8mm, 3.0mm, 3.2mm, 3.5mm, 3.8mm, 4.0mm, etc. Within this size range, the encapsulating carrier can resist the physical erosion of the incoming water flow and the extrusion and abrasion between media, while ensuring that the internal pores have excellent mass transfer efficiency, ensuring that dissolved oxygen and various nutrient substrates can smoothly penetrate into the interior of the microspheres, maintaining the high activity of deep microorganisms.

[0058] In some embodiments, the heterotrophic nitrifying-aerobic denitrifying bacteria include *Pseudomonas schrenckii*.

[0059] In some embodiments, the microalgae are selected from one or more combinations of Chlorella, Scenedesmus, Chlamydomonas, and Nostoc. These microalgae exhibit good adaptability to low-light environments. These two organisms constitute a highly efficient metabolic feedback system within the microsphere: the microalgae release oxygen and organic secretions through photosynthetic carbon fixation, providing in-situ electron acceptors and endogenous carbon sources for Pseudomonas schistosomiasis; while the carbon dioxide produced by the mineralization metabolism of Pseudomonas schistosomiasis is supplied back to the microalgae, thus effectively overcoming the problem of limited denitrification caused by carbon source scarcity in rainwater runoff.

[0060] In some embodiments, the embedding matrix of the algal microspheres includes a cross-linked network of polyvinyl alcohol and boric acid, and sodium alginate.

[0061] To achieve secure immobilization of the aforementioned bacteria and algae, the embedding matrix of the microspheres comprises a three-dimensional cross-linked network formed by the acetalization reaction of polyvinyl alcohol and boric acid, in which sodium alginate is doped. The polyvinyl alcohol cross-linked network endows the microspheres with excellent mechanical compressive strength, while the presence of sodium alginate provides an excellent biocompatibility internal buffer space, avoiding damage to the activity of the bacteria and algae cells during the cross-linking and solidification process.

[0062] In some embodiments, the microspheres contain a microscale dissolved oxygen gradient, with the dissolved oxygen concentration near the surface of the microspheres being 1.5 mg / L to 3.0 mg / L (e.g., 1.5 mg / L, 1.6 mg / L, 1.8 mg / L, 2.0 mg / L, 2.2 mg / L, 2.4 mg / L, 2.5 mg / L, 2.8 mg / L, 3.0 mg / L, etc.), decreasing towards the center of the microspheres to 0.2 mg / L to 0.8 mg / L (e.g., 0.20 mg / L, 0.25 mg / L, 0.30 mg / L, 0.40 mg / L, 0.50 mg / L, 0.55 mg / L, 0.60 mg / L, 0.70 mg / L, 0.80 mg / L, etc.).

[0063] Based on the aforementioned encapsulation structure and biological metabolic characteristics, a stable microscale dissolved oxygen gradient is formed and maintained within the microspheres. The dissolved oxygen concentration near the microsphere surface is relatively high, typically ranging from 1.5 mg / L to 3.0 mg / L, primarily supporting heterotrophic aerobic degradation and nitrification. Due to diffusion resistance during oxygen inward transfer and consumption by external microorganisms, the dissolved oxygen concentration gradually decreases to a low-oxygen state of 0.2 mg / L to 0.8 mg / L as the microsphere moves towards its central region. This microenvironment significantly promotes aerobic denitrification. Specifically, the high dissolved oxygen environment on the microsphere surface effectively stimulates the activity of ammonia monooxygenase (AMO), enhancing heterotrophic nitrification; while the low-oxygen microenvironment inside increases the activity of periplasmic nitrate reductase (NAP) and nitrite reductase (NIR), ensuring the smooth progress of aerobic denitrification. This surface-to-interior oxygen distribution gradient achieves simultaneous nitrogen and phosphorus removal on a single microsphere.

[0064] In some embodiments, the control unit controls a wet-dry alternation cycle including: controlling the flooding period to be 2h~6h (e.g., 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6.0h, etc.), and controlling the drying period to be 4h~12h (e.g., 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.).

[0065] A moderate flooding period ensures sufficient reaction between pollutants and the surfaces of microspheres and fillers; while a sufficient drying period allows the wetland to be completely emptied, enabling the external atmosphere to penetrate deep into the system for efficient natural reoxygenation. This allows aerobic microorganisms to quickly restore their metabolic activity and effectively controls the risk of pore blockage caused by excessive biomass accumulation.

[0066] refer to Figure 2 This application also provides a method for preparing microspheres of bacteria and algae, used to prepare microspheres of bacteria and algae in the aforementioned symbiotic constructed wetland system. This preparation method, through specific biological mixing, polymer encapsulation, and environmental acclimatization strategies, endows the molded material with extremely high mechanical strength, excellent mass transfer performance, and outstanding adaptability to low-light environments. Specifically, it includes the following steps: Step S1: Mix the activated heterotrophic nitrifying-aerobic denitrifying bacteria solution with the microalgae solution to obtain a bacterial-algae mixture.

[0067] Before performing this step, the selected target bacteria and microalgae are typically cultured independently until they enter the logarithmic growth phase to ensure that the cells used have the most vigorous metabolic proliferation capacity and intact cell membrane structure. The mixing of the two aims to achieve uniform dispersion at the cell level in the liquid phase, thereby laying the spatial distribution foundation for establishing efficient carbon and nitrogen metabolic feedback relationships on a very small spatial scale.

[0068] Step S2: The bacterial-algae mixture is mixed with a solution containing polyvinyl alcohol and sodium alginate to prepare an encapsulation precursor solution.

[0069] In this system, polyvinyl alcohol serves as the core precursor for forming the microsphere skeleton, aiming to provide high-strength structural support; while sodium alginate, as a natural high-molecular-weight polysaccharide, with its excellent hydrophilicity and biocompatibility, can form a flexible buffer microenvironment in the uncrosslinked polymer chain segments, effectively protecting fragile microbial cells from the osmotic pressure impact and mechanical compression of subsequent chemical reaction processes.

[0070] Step S3: The embedding precursor solution is dropped into a crosslinking solution containing boric acid, and crosslinking and curing are performed to obtain microspheres.

[0071] During this process, as the precursor liquid is introduced, the hydroxyl groups on the polyvinyl alcohol molecular chains rapidly undergo acetalization and cross-linking with boric acid, instantly constructing a dense three-dimensional polymer network structure that anchors the mixed bacterial and algal cells within in situ. Under surface tension, the droplets naturally form spheres. The solidified cross-linked network not only endows the microspheres with excellent resistance to hydrodynamic erosion, but its abundant micropores also provide unobstructed mass transfer channels for the penetration of the external matrix and the discharge of internal metabolic products.

[0072] Step S4: The formed microspheres are activated and cultured, and the light intensity is gradually reduced in the later stage of activation to acclimate them to weak light.

[0073] Because the chemical cross-linking process causes a certain stress response in cells, the initial activation culture can promote the repair and recolonization of damaged microorganisms in the internal channels of the microspheres, establishing a stable symbiotic state. Crucially, in the middle and later stages of activation, by artificially simulating a stepwise decrease in ambient light intensity (i.e., low-light adaptive acclimatization), the microalgae inside the microspheres are forced to adapt to the low-photon flux environment through physiological adjustments (such as increasing the synthesis of light-harvesting pigments or adjusting the photosynthetic system architecture).

[0074] The “low-light adaptive acclimatization” described in this article refers to a specific culture process in which photosynthetic microorganisms are subjected to mild environmental stress by gradually reducing the intensity of ambient light, thereby inducing physiological or genetic adaptive changes, so that they can maintain stable and efficient photosynthetic oxygen production activity when faced with low light conditions (such as cloudy or rainy weather or deep water bodies).

[0075] The microspheres prepared through the above-mentioned low-light adaptation acclimatization steps can effectively overcome the high dependence of conventional photosynthetic water treatment systems on strong light. Even under non-ideal lighting conditions or cloudy and rainy weather in actual rainwater treatment facilities, they can still meet the denitrification oxygen demand of internal bacteria through continuous oxygen production by microalgae, effectively improving the stability of the ecosystem in practical engineering applications.

[0076] In some embodiments, the solution containing polyvinyl alcohol and sodium alginate has a mass fraction of 8% to 10% for polyvinyl alcohol and a mass fraction of 0.5% to 1% for sodium alginate. For example, it can be 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, etc.

[0077] This ratio range ensures that the polymer solution possesses suitable rheological properties, avoiding both poor mechanical strength of the microspheres due to excessively low polyvinyl alcohol concentration and excessive internal pore blockage and mass transfer resistance caused by excessively high concentration. Simultaneously, the appropriate amount of sodium alginate provides good hydrophilicity and flexible buffering in the cross-linked network, which is beneficial for maintaining the physiological activity of the encapsulated microorganisms.

[0078] In some embodiments, the volume ratio of the activated heterotrophic nitrifying-aerobic denitrifying bacteria solution to the microalgae solution in the bacterial-algae mixture is 2:1. During the mixing of the bacterial and microalgae solutions, 0.5%–1% glycerol or trehalose can be added as a cell protectant to resist osmotic pressure damage during subsequent cross-linking processes; simultaneously, 0.1%–0.5% activated carbon powder can be added to enrich the pore structure inside the microspheres and improve the physicochemical stability of the microenvironment. This inoculation ratio ensures that the microspheres are dominated by a bacterial community performing degradation and denitrification functions, supplemented by microalgae of appropriate biomass to provide in-situ photosynthetic oxygen production. This configuration effectively avoids internal space competition and light self-shielding effects caused by an excessively high proportion of microalgae, constructing a stable oxygen supply and consumption balance system.

[0079] In some embodiments, the pH of the boric acid-containing crosslinking solution is 6.5–7.0; for example, it can be 6.5, 6.55, 6.6, 6.65, 6.7, 6.75, 6.8, 6.85, 6.9, 7.0, etc. By constructing a near-neutral, mild chemical crosslinking environment, the acid shock and structural damage caused to bacterial and algal cells by conventional acidic boric acid solutions are effectively avoided, thereby ensuring a high cell survival rate inside the molded microspheres.

[0080] In some embodiments, the step of dropping the embedding precursor solution into the crosslinking solution containing boric acid specifically includes: dropping the embedding precursor solution into the crosslinking solution at a dropping rate of 1 mL / min to 2 mL / min (e.g., 1.0 mL / min, 1.1 mL / min, 1.2 mL / min, 1.4 mL / min, 1.5 mL / min, 1.6 mL / min, 1.8 mL / min, 1.9 mL / min, 2.0 mL / min, etc.) at a dropping height of 10 cm to 20 cm (e.g., 10 cm, 11 cm, 12 cm, 14 cm, 15 cm, 16 cm, 18 cm, 19 cm, 20 cm, etc.).

[0081] An appropriate dropping velocity ensures that droplets form independently and uniformly, preventing adhesion; while a free-fall height of 10cm to 20cm provides sufficient time for the droplets to fall in the air and contract into regular spheres based on surface tension, while limiting the kinetic energy when impacting the cross-linked liquid surface, preventing droplet breakage or deformation. This combination of parameters significantly improves the sphericity and particle size uniformity of microspheres prepared in batches.

[0082] In some preferred embodiments of this application, specific parameter settings are made for the dry-wet alternation time cycle in the operation method to further optimize the system's pollutant removal efficiency and maintain long-term operational stability. The periodic control operations in the operation method can be independently executed by the automated control unit according to a preset time program.

[0083] Specifically, the operation method for controlling stormwater runoff pollution uses the aforementioned bacterial-algae symbiotic constructed wetland system, and the operation method includes at least one periodically alternating flooding step and drying step.

[0084] (1) Flooding step: control the water inlet device to open, introduce the rainwater runoff to be treated into the wetland bed in a waterfall manner, and maintain the wetland bed in a flooded state during the preset flooding period; wherein, the rainwater runoff flows through the light-transmitting area and the non-light-transmitting area in sequence, so as to use the light and the oxygen introduced by the waterfall to drive the bacteria and algae microspheres to carry out nitrogen and phosphorus removal reaction.

[0085] In some implementations, the flooding period is 2 to 6 hours. For example, it can be 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, etc.

[0086] This period serves as the primary contact phase for pollutant retention and biochemical degradation. Its duration is sufficient to ensure that dissolved substrates in the water (such as organic matter, nitrogen and phosphorus nutrients, etc.) fully diffuse into the biofilm and reaction medium, where they are effectively absorbed and transformed by microorganisms. Simultaneously, limiting the flooding period to within 6 hours effectively prevents the system from falling into a deep anaerobic state due to prolonged immersion, thus mitigating the engineering risks of anaerobic fermentation producing foul-smelling gases and the significant inactivation of aerobic microorganisms.

[0087] (2) Drying step: After the flooding period ends, control the water inlet device to stop water intake and control the drainage device to drain the water inside the wetland bed; maintain the wetland bed in an empty state during the preset drying period so that external air can enter the wetland bed for atmospheric reoxygenation.

[0088] The drying period is 4 to 12 hours. For example, it can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc.

[0089] During this period, the physical pores inside the system are refilled with external air, allowing for efficient atmospheric natural diffusion and reoxygenation. This 4-12 hour rest period not only provides ample oxygen for internal aerobic microorganisms (such as nitrifying bacteria) to restore their physiological metabolic activity and build up their enzymatic reaction capacity for degradation in the next cycle, but also, the oxygen-rich and relatively dry environment helps to oxidize and degrade excessively accumulated metabolic residues within the biofilm, effectively inhibiting biological clogging of the packing pores and ensuring the long-term stability of the system's hydraulic conductivity.

[0090] This reasonable ratio of flooding and drying time parameters creates a rhythmic aerobic / anoxic dynamic microenvironment within the system, achieving the multiple oxidation-reduction conditions required for nitrogen and phosphorus removal processes with low operating energy consumption without the need for additional mechanical aeration equipment.

[0091] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0092] Example 1 This embodiment examines the preparation of microspheres from bacteria and algae under intermediate conditions of main raw materials and important process parameters, as well as the system operation effect.

[0093] A dry-wet alternating constructed wetland system based on bacterial and algal microspheres and its operation method are described below: (1) Preparation of bacterial-algae mixture: The bacterial-algae mixture was prepared by mixing the Pseudomonas schlegelii solution in the logarithmic growth phase with Chlorella solution at a volume ratio of 2:1.

[0094] (2) Preparation of the embedding precursor solution: Weigh polyvinyl alcohol (PVA) and sodium alginate (SA), dissolve them in deionized water, and after heating and sterilization, obtain a polymer solution with a polyvinyl alcohol mass fraction of 9% and a sodium alginate mass fraction of 0.75%. Mix this polymer solution with the above-mentioned bacterial-algae mixture, add 0.5% glycerol and 0.2% activated carbon powder by mass, and stir evenly to prepare the embedding precursor solution.

[0095] (3) Drop cross-linking molding: Prepare a cross-linking solution containing boric acid and adjust the pH of the cross-linking solution to 6.8. Under stirring conditions, drop the pre-embedding solution into the cross-linking solution at a dropping rate of 1.5 mL / min and a dropping height of 15 cm. After solidification for 12 h, wash with water to obtain algal microspheres with a particle size of about 3 mm.

[0096] (4) Adaptation to weak light: The formed microspheres were placed in a nutrient solution for activation and culture. In the later stage of activation, the light intensity was gradually reduced from 2000 Lux to 1000 Lux for 3 days.

[0097] (5) System Construction and Operation: Microspheres were filled into the light-transmitting area (20 cm high); the non-light-transmitting area (40 cm high) was filled with a mixture of large-particle-size zeolite (10 mm) and small-particle-size zeolite (5 mm); the support layer (15 cm high) was filled with pebbles with a particle size of 30 mm. Initial rainwater was introduced, and the flooding period was controlled to be 4 hours and the drying period to be 8 hours within one cycle.

[0098] Example 2 This embodiment examines the parameter range of polyvinyl alcohol based on Example 1.

[0099] The specific steps are basically the same as in Example 1, except that in step 2, the mass fraction of polyvinyl alcohol is controlled to be 8%.

[0100] Example 3 This embodiment examines the parameter range of polyvinyl alcohol based on Example 1.

[0101] The specific steps are basically the same as in Example 1, except that in step 2, the mass fraction of polyvinyl alcohol is controlled to be 10%.

[0102] Example 4 This embodiment examines the pH parameter range of the crosslinking solution, based on Example 1.

[0103] The specific steps are basically the same as in Example 1, except that in step 3, the pH of the crosslinking solution is adjusted to 6.5.

[0104] Example 5 This embodiment examines the pH parameter range of the crosslinking solution, based on Example 1.

[0105] The specific steps are basically the same as in Example 1, except that in step 3, the pH of the crosslinking solution is adjusted to 7.0.

[0106] Example 6 This embodiment examines alternative microalgae raw materials based on Example 1.

[0107] The specific steps are basically the same as in Example 1, except that in step 1, Chlorella is replaced with Scenedesmus of the same volume.

[0108] Example 7 This embodiment examines alternative combinations of filler materials based on Embodiment 1.

[0109] The specific steps are basically the same as in Example 1, except that in step 5, the non-transparent area is filled with a mixture of 10 mm ceramsite and 5 mm limestone.

[0110] Example 8 This embodiment examines the parameters for alternating dry and wet operation, based on Embodiment 1.

[0111] The specific steps are basically the same as in Example 1, except that in step 5, the flooding period is controlled to be 6 hours and the drying period to be 12 hours within one cycle.

[0112] Example 9 This embodiment examines the parameter range of sodium alginate based on Example 1.

[0113] The specific steps are basically the same as in Example 1, except that in step (2), the mass fraction of sodium alginate is controlled to be 0.5%.

[0114] Example 10 This embodiment examines the parameter range of sodium alginate based on Example 1.

[0115] The specific steps are basically the same as in Example 1, except that in step (2), the mass fraction of sodium alginate is controlled to be 1.0%.

[0116] Comparative Example 1 This comparative example is based on Example 1, but the core microalgae components have been removed.

[0117] The specific steps are basically the same as in Example 1, except that in step 1, no Chlorella solution is added, and only Pseudomonas schrenckii solution is used for encapsulation.

[0118] Comparative Example 2 This comparative example, based on Example 1, exceeds the parameter range of polyvinyl alcohol.

[0119] The specific steps are basically the same as in Example 1, except that in step 2, the mass fraction of polyvinyl alcohol is controlled to be 5%.

[0120] Comparative Example 3 This comparative example, based on Example 1, exceeds the parameter range of pH of the crosslinking solution.

[0121] The specific steps are basically the same as in Example 1, except that in step 3, a conventional boric acid crosslinking solution with unadjusted pH (pH 4.0) is used.

[0122] Comparative Example 4 This comparative example omits the core domestication step in the process, based on Example 1.

[0123] The specific steps are basically the same as in Example 1, except that the operation of "gradually reducing the light intensity from 2000 Lux to 1000 Lux in the later stage of activation" in step 4 is removed, and the microspheres are put into use directly after activation under normal strong light.

[0124] Comparative Example 5 This comparative example differs from Example 1 in that it modifies the operating method.

[0125] The specific steps are basically the same as in Example 1, except that in step 5, the draining step is not performed, and the wetland bed adopts a continuous flooding and water intake operation mode.

[0126] Comparative Example 6 This comparative example, based on Example 1, changed the core biological ratio to examine the case where the bacterial culture ratio was too low.

[0127] The specific steps are basically the same as in Example 1, except that in step (1), the volume ratio of heterotrophic nitrification-aerobic denitrification bacteria solution to microalgae solution is changed to 1:1.

[0128] Comparative Example 7 This comparative example, based on Example 1, changed the core biological ratio to examine the case where the bacterial solution ratio was too high.

[0129] The specific steps are basically the same as in Example 1, except that in step (1), the volume ratio of heterotrophic nitrification-aerobic denitrification bacteria solution to microalgae solution is changed to 3:1.

[0130] Comparative Example 8 This comparative example, based on Example 1, exceeds the parameter range of sodium alginate.

[0131] The specific steps are basically the same as in Example 1, except that in step (2), the mass fraction of sodium alginate is controlled to be 0.1%.

[0132] Comparative Example 9 This comparative example, based on Example 1, exceeds the parameter range of sodium alginate.

[0133] The specific steps are basically the same as in Example 1, except that in step (2), the mass fraction of sodium alginate is controlled to be 1.5%.

[0134] Comparative Example 10 This comparative example differs from Example 1 in that the physical molding parameters have been modified.

[0135] The specific steps are basically the same as in Example 1, except that in step (3), the embedding precursor solution is dropped into the crosslinking solution at a dropping speed of 3 mL / min and a dropping height of 5 cm.

[0136] Experimental testing and results analysis: 1. Experimental Method: The systems prepared in Examples 1-8 and Comparative Examples 1-5 were used to conduct continuous treatment experiments simulating rainfall runoff with artificial water distribution. The water quality indicators ranged as follows: COD 150~200 mg / L, TN (total nitrogen) 15~20 mg / L, TP (total phosphorus) 1.5~2.0 mg / L, and the ambient light was simulated under low light conditions (800~1000 Lux) during cloudy or rainy days. After the system ran continuously for 30 days, the effluent quality was measured to calculate the average removal rate of pollutants. Simultaneously, the mechanical compressive strength of each group of microspheres was tested (the maximum compressive stress was determined using a computer-controlled electronic universal testing machine).

[0137] 2. Experimental Results: The performance test data of each embodiment and comparative example are summarized in Table 1.

[0138] Table 1. Performance test results of each embodiment and comparative example

[0139] 3. Results Analysis: (1) As can be seen from the comparison between Examples 1, 2, and 3 and Comparative Example 2, a PVA concentration between 8% and 10% can balance mass transfer efficiency and mechanical strength. In Comparative Example 2, the microspheres broke apart due to the low concentration, resulting in the loss of internal microorganisms and a general decrease in removal rates.

[0140] (2) The comparison between Example 1 and Comparative Examples 1 and 4 shows that the introduction of microalgae and the adaptation to low light conditions are key to maintaining denitrification efficiency under low light conditions. Comparative Example 1 lacked microalgal oxygen production, and Comparative Example 4 failed to adapt to the low light environment. Neither of them could form a suitable local aerobic microenvironment, which led to the inhibition of nitrification by Pseudomonas stearothermiae, and the TN removal rates dropped to 41.2% and 55.4%, respectively. In addition, Comparative Example 3 demonstrated that adjusting the pH of the crosslinking solution to 6.5-7.0 could avoid acid shock and effectively protect cell viability.

[0141] (3) The comparison between Example 1 and Comparative Example 5 intuitively reflects the engineering value of alternating wet and dry operation. Under continuous flooding conditions, the pores of the internal packing in Comparative Example 5 were filled with water, preventing atmospheric oxygen from diffusing. The system rapidly lost its aerobic metabolic capacity, and the TN removal rate plummeted to 30.5%, indicating that alternating wet and dry operation is a necessary means to achieve low-energy oxygen supply in the system. Example 7, by introducing limestone packing and utilizing the chemical precipitation mechanism of calcium salts, further increased the TP removal rate to 92.4%, demonstrating the excellent effect of synergistic phosphorus removal through packing gradation.

[0142] (4) Examination of biological ratio: The comparison between Example 1 and Comparative Examples 6 and 7 shows that a volume ratio of bacteria to microalgae of 2:1 is the key to maintaining the microecological balance. In Comparative Example 6, the proportion of microalgae was too high, which caused internal light self-shading and squeezed the living space of bacteria, resulting in a TN removal rate of 74.2%. In Comparative Example 7, the proportion of microalgae was too low, resulting in insufficient in-situ oxygen supply and inhibiting the activity of ammonia monooxygenase, which led to a significant decline in denitrification efficiency.

[0143] (5) Examination of sodium alginate concentration: The comparison between Examples 1, 9, and 10 and Comparative Examples 8 and 9 shows that sodium alginate provides a good hydrophilic buffer in the range of 0.5% to 1%. In Comparative Example 8, the concentration was too low (0.1%), which caused the cells to be damaged by physical compression during the cross-linking process. In Comparative Example 9, the concentration was too high (1.5%), which caused the precursor solution to become viscous. After solidification, the pores were blocked, the mass transfer resistance increased sharply, and the penetration of the contaminating substrate was affected.

[0144] (6) Examination of the droplet molding process: Comparative Example 10 deviated from the preferred hydrodynamic parameters. Due to the excessively fast droplet acceleration (3 mL / min) and insufficient height (5 cm), the droplet failed to fully contract due to surface tension before falling into the crosslinking liquid, resulting in the formed microspheres having a tail-like or flattened shape. This irregular shape caused its mechanical strength to drop significantly to 0.08 MPa, making it extremely easy to break under the scouring of water flow, further confirming the technical necessity of limiting the molding parameters to ensure the physical stability of the material.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fungal-algae symbiotic constructed wetland system, characterized in that, include: Wetland bed, water inlet device, drainage device and control unit; The wetland bed is divided into a light-transmitting zone and a non-light-transmitting zone at least from top to bottom along the water flow direction; the light-transmitting zone is filled with bacterial and algal microspheres; the bacterial and algal microspheres are co-embedded bodies containing heterotrophic nitrifying-aerobic denitrifying bacteria and microalgae; the non-light-transmitting zone is filled with packing material. The water inlet device is located at the upper part of the wetland bed and is used to introduce water to be treated into the light-transmitting area; The drainage device is located at the lower part of the wetland bed and is used to drain the treated water and empty the water inside the wetland bed. The control unit is connected to the water inlet device and the drainage device respectively, and is used to control the start and stop of water inlet and drainage so that the wetland bed can operate alternately periodically between the flooding period and the drying period.

2. The constructed wetland system with symbiotic bacteria and algae as described in claim 1, characterized in that, The wetland bed is divided into a water replenishment layer, a light-transmitting zone, a non-light-transmitting zone, and a support layer from top to bottom along the water flow direction.

3. The constructed wetland system with symbiotic bacteria and algae as described in claim 2, characterized in that, The outlet of the water inlet device is located above the water replenishment layer and is configured to introduce the water to be treated in a cascading manner; the control unit is configured to control the water replenishment layer to maintain a submerged water depth during the flooding period.

4. The constructed wetland system with symbiotic bacteria and algae as described in claim 2, characterized in that, The height of the light-transmitting area is 10cm to 30cm; and / or, The height of the non-transparent area is 30cm~50cm; and / or, The filler in the non-transparent area comprises large-particle-size filler with a particle size of 8mm to 15mm and small-particle-size filler with a particle size of 4mm to 6mm, which are graded and filled; and / or, The height of the supporting layer is 10cm to 20cm; and / or, The support layer is filled with support filler with a particle size of 20mm to 40mm.

5. The constructed wetland system with symbiotic bacteria and algae as described in claim 4, characterized in that, The filler in the non-transparent area is selected from at least one of zeolite, ceramsite, and limestone; and / or, The supporting filler in the support layer is pebbles and / or crushed stone.

6. The constructed wetland system with symbiotic bacteria and algae as described in claim 1, characterized in that, The particle size of the algal microspheres is 2mm~4mm; and / or, The heterotrophic nitrifying-aerobic denitrifying bacteria include *Pseudomonas schistosomiasis*; and / or... The microalgae are selected from one or more combinations of Chlorella, Scenedesmus, Chlamydomonas, and Nostoc; and / or, The encapsulation matrix of the algal microspheres includes a cross-linked network of polyvinyl alcohol and boric acid, and sodium alginate; and / or, The microspheres contain a microscale dissolved oxygen gradient, with a dissolved oxygen concentration of 1.5 mg / L to 3.0 mg / L near the surface of the microspheres, decreasing to 0.2 mg / L to 0.8 mg / L towards the center of the microspheres. And / or, The control unit controls a wet-dry alternation cycle including controlling the flooding period to be 2h~6h and the drying period to be 4h~12h.

7. A method for preparing microspheres of bacteria and algae, characterized in that, The method for preparing microspheres of bacteria and algae in the bacterial-algae symbiotic constructed wetland system as described in any one of claims 1-6 comprises: The activated heterotrophic nitrifying-aerobic denitrifying bacteria solution was mixed with the microalgae solution to obtain a bacterial-algae mixture. The bacterial-algae mixture was mixed with a solution containing polyvinyl alcohol and sodium alginate to prepare an encapsulation precursor solution. The embedding precursor solution was dropped into a crosslinking solution containing boric acid, and crosslinking and curing were performed to obtain microspheres. The formed microspheres were activated and cultured, and the light intensity was gradually reduced in the later stage of activation to acclimate them to weak light.

8. The method for preparing algal microspheres as described in claim 7, characterized in that, In the solution containing polyvinyl alcohol and sodium alginate, the mass fraction of polyvinyl alcohol is 8%~10%, and the mass fraction of sodium alginate is 0.5%~1%; and / or, In the bacterial-algae mixture, the volume ratio of the activated heterotrophic nitrifying-aerobic denitrifying bacteria solution to the microalgae solution is 2:1; and / or, The pH of the crosslinking solution containing boric acid is 6.5-7.0; and / or, The step of dripping the embedding precursor solution into the crosslinking solution containing boric acid specifically includes: dripping the embedding precursor solution into the crosslinking solution at a dripping rate of 1 mL / min to 2 mL / min and a dripping height of 10 cm to 20 cm.

9. An operational method for controlling stormwater runoff pollution, characterized in that, The method of operating the constructed wetland system of symbiotic bacteria and algae as described in any one of claims 1-6 includes at least one periodically alternating flooding step and a drying step: Flooding Steps: The water inlet device is turned on to introduce the rainwater runoff to be treated into the wetland bed in a cascading manner, and the wetland bed is kept submerged during the preset flooding period; wherein, the rainwater runoff flows sequentially through the light-transmitting area and the non-light-transmitting area, so as to use the light and the oxygen introduced by the cascading method to drive the bacteria and algae microspheres to carry out nitrogen and phosphorus removal reactions. Drying process: After the flooding period ends, the water inlet device is controlled to stop water intake, and the drainage device is controlled to drain the water inside the wetland bed. During the preset drying period, the wetland bed is kept in an empty state so that outside air can enter the wetland bed for atmospheric reoxygenation.

10. The operating method for stormwater runoff pollution control as described in claim 9, characterized in that, The flooding period is 2 hours to 6 hours; and / or, The drying period is 4 to 12 hours.

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