Long-acting phosphorus removal method of wetland coupling anti-pollution and rhizosphere activation

Abstract

This invention discloses a long-term phosphorus removal method for wetlands that couples anti-pollution and rhizosphere activation; belonging to the field of constructed wetland water treatment technology, the method includes the following steps: constructing a vertical flow constructed wetland reactor and filling it with lanthanum-chitosan-modified zeolite packing material; initially introducing slightly polluted river or lake water, using the packing material to release alkaline substances to maintain a pH of 11.0–12.0, and rapidly fixing phosphorus through chemical precipitation; after the effluent pH drops to the normal range, emergent plants are planted, using low phosphorus stress to induce the roots to secrete organic acids, neutralizing residual alkalinity and dissolving insoluble phosphorus on the packing material surface, thus regenerating active sites; simultaneously, utilizing the positively charged microenvironment of chitosan quaternary ammonium salt on the packing material surface and the synergistic antibacterial mechanism of the lanthanum-loaded nanostructure, microbial attachment and extracellular polymer secretion are inhibited, preventing bioclogging. This invention achieves efficient and long-term phosphorus removal from slightly polluted river or lake water through the synergistic effect of high-alkalinity start-up, rhizosphere activation, and anti-biofouling, extending the system's operating cycle.

Description

Technical Field

[0001] This invention relates to a micro-polluted river and lake water treatment technology, belonging to the field of constructed wetland water treatment technology. Specifically, it relates to a long-term phosphorus removal method in wetlands that couples anti-pollution and rhizosphere activation. Through the synergistic effect of high-alkalinity start-up operation, rhizosphere micro-ecological activation, and the anti-biological pollution properties of the packing surface, it achieves efficient and long-term removal of phosphorus from micro-polluted river and lake water. Background Technology

[0002] Constructed wetlands are widely used in rural decentralized treatment of slightly polluted rivers and lakes, agricultural non-point source pollution control, and landscape water purification due to their advantages such as low operating costs, eco-friendliness, ease of operation, and ability to utilize slightly polluted river and lake water resources. In constructed wetland purification systems, the packing material, as the core carrier for interaction between slightly polluted river and lake water and plants and microorganisms, directly affects the phosphorus removal efficiency of the system due to its adsorption performance and stability. Plants, as an important component of ecological purification, achieve phosphorus migration and transformation through root absorption and enrichment. The synergistic effect of both is key to improving the phosphorus removal efficiency of constructed wetlands.

[0003] However, existing technologies do not address the bioclogging problem of modified fillers during the long-term operation of constructed wetlands. Studies have shown that the accumulation of extracellular polymeric substances (EPS) secreted by microorganisms on the surface of constructed wetland substrates is one of the main causes of substrate clogging. Bioclogging is a multi-stage, continuous process: it begins with the initial attachment of bacteria to the substrate surface, followed by bacterial proliferation and the massive secretion of EPS, ultimately forming a dense biofilm layer. This biofilm layer not only physically clogs substrate pores and reduces hydraulic conductivity, but also occupies active sites for phosphorus adsorption on the substrate surface, leading to a rapid decrease in phosphorus removal efficiency and a significant shortening of substrate lifespan. Therefore, developing novel substrates that combine efficient phosphorus removal with resistance to biofilm fouling, inhibiting initial bacterial adhesion and blocking excessive EPS secretion at the source, is of great significance for achieving long-term stable operation of constructed wetlands.

[0004] Chinese patent CN 118993356A (publication date: November 22, 2024) discloses a phosphorus removal and antibacterial modified zeolite filler, its preparation method, and its application. This patent prepares a lanthanum-chitosan-zeolite composite material (LCZ-C) by compounding quaternized chitosan with lanthanum ions and loading them onto the surface of natural zeolite. This composite material exhibits high adsorption performance for phosphates, with a maximum adsorption capacity of 46.69 mg / g, approximately 16 times higher than that of natural zeolite; under an initial phosphorus concentration of 2 mg / L, its phosphorus removal rate exceeds 93%. The patent explicitly states that the filler can be used in the field of water phosphorus removal and purification, providing a highly efficient functional material for the treatment of phosphorus pollution in water bodies. However, its technical solution mainly focuses on the adsorption and antibacterial properties of the filler itself, without addressing the synergistic mechanism between the modified system and constructed wetland plants, nor disclosing the promoting effect of the filler on plant root growth and the overall phosphorus removal efficiency of the system. Meanwhile, the material exhibits a significant inhibitory effect on microorganisms such as Escherichia coli, thereby helping to alleviate the problem of bioclogging in constructed wetland systems. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a long-term phosphorus removal method for wetlands that combines anti-fouling and rhizosphere activation. This method involves constructing a wetland reactor with a specific structure and employing staged operation control to achieve efficient phosphorus removal from slightly polluted rivers and lakes. Simultaneously, it utilizes the anti-biofouling properties of the modified packing surface to inhibit initial bacterial adhesion and extracellular polymer secretion from the source through an electrostatic-mechanical synergistic antibacterial mechanism. This prevents excessive biofilm accumulation, protects the active sites of the packing, and extends the system's operational life.

[0006] The technical solution of this invention is: a long-term phosphorus removal method for wetlands that couples pollution resistance and rhizosphere activation, comprising the following steps: Step (1) Construct a cylindrical vertical flow constructed wetland reactor. Inside the vertical flow constructed wetland reactor, from bottom to top, a gravel support layer, a modified zeolite packing layer, and a fine sand covering layer are arranged sequentially. Step (2) High-alkali phosphorus fixation treatment: Slightly polluted river and lake water is continuously introduced into the vertical flow constructed wetland reactor, causing the modified zeolite packing to release alkaline substances, thereby maintaining the pH of the system effluent in the range of 11.0 to 12.0. Under this condition, rapid fixation of phosphorus in the water is achieved (using the initial release of alkaline substances from the modified zeolite packing to maintain a high alkalinity environment in the water, and fixing phosphorus in the water through chemical precipitation mediated by metal ions). Step (3) Water quality control and plant planting: Continuously monitor the pH of the effluent. Once the pH of the effluent drops to a normal range suitable for plant growth, plant emergent plants in the designated area of ​​the vertical flow constructed wetland reactor. Step (4) Complete in-situ rhizosphere activation and synergistic phosphorus removal: Utilize the low phosphorus stress environment formed by the depletion of phosphorus in the water body due to high alkali fixation in the early stage to induce the spontaneous secretion of organic acids by the roots of emergent plants in the artificial wetland, neutralize the residual alkaline substances in the system and dissolve the insoluble phosphorus on the surface of the packing material, thereby realizing the regeneration of the active sites on the surface of the packing material. Step (5) Maintain long-term stable operation of the system: Utilize the positively charged microenvironment of chitosan quaternary ammonium salt on the surface of the modified zeolite filler and the mechanical / electrostatic synergistic antibacterial mechanism of lanthanum-loaded nanostructure to continuously inhibit excessive microbial attachment and EPS secretion on the matrix surface, prevent biological blockage and occupation of active sites, and maintain the long-term stability of the system's phosphorus removal efficiency.

[0007] Furthermore, the cylindrical vertical flow constructed wetland reactor described in step (1) is made of plexiglass; its vertical section has a diameter of 0.20 meters and a height of 0.70 meters; its packing height is 0.6 meters; and the gravel support layer, modified zeolite packing layer and fine sand cover layer are respectively filled with gravel, lanthanum chitosan modified zeolite packing and fine sand.

[0008] Furthermore, the gravel support layer is divided into two layers: the bottom layer has a particle size of 20 to 30 mm and a filling height of 0.08 to 0.15 m, and the top layer has a particle size of 5 to 10 mm and a filling height of 0.03 to 0.08 m. The particle size of the modified zeolite filler layer is set to 5 to 8 mm and the filling height is 0.2 to 0.5 m; The filling height of the fine sand covering layer is 0.1 to 0.2 meters.

[0009] Furthermore, the phosphorus-removing and antibacterial modified zeolite filler (lanthanum-chitosan modified zeolite filler) is prepared by mixing and granulating lanthanum-chitosan-zeolite composite material with cement, with a particle size of 5 to 8 mm and a cement mass fraction of 50%. The lanthanum-chitosan-modified zeolite filler has anti-biofouling properties. Through the electrostatic interaction between the positively charged groups of chitosan quaternary ammonium salt and the bacterial cell membrane, and the mechanical stress effect of the surface nanostructure formed by lanthanum loading on microorganisms, bacterial attachment and extracellular polymer secretion are synergistically inhibited, thereby alleviating matrix biofouling and protecting the active sites on the filler surface.

[0010] Furthermore, in the initial stage of use of the modified zeolite filler described in step (2), the pH of the water body is maintained between 11.0 and 12.0, generating insoluble precipitates such as hydroxyapatite and lanthanum phosphate.

[0011] Furthermore, the emergent plants of the artificial wetland in step (3) are selected from one or more combinations of yellow iris, reed, cattail, canna, umbrella sedge and loosestrife.

[0012] Furthermore, the emergent plants in the artificial wetland planted in step (3) must be in the same growth stage and have consistent growth, and the biomass deviation between plants should be controlled within 10%.

[0013] Further, the organic acid mentioned in step (4) is at least one of succinic acid, lactic acid, fumaric acid, propionic acid, butyric acid, citric acid and oxalic acid.

[0014] Furthermore, the method extends the effective operating cycle of the constructed wetland system and reduces the frequency of packing replacement by inhibiting excessive biofilm formation on the packing surface.

[0015] Furthermore, this method was applied to the purification of slightly polluted urban water bodies, with the total phosphorus concentration in the introduced slightly polluted river and lake water being 0.05 to 0.5 mg / L, and the hydraulic retention time being controlled at 2 to 3 days.

[0016] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention effectively improves the removal of total phosphorus from slightly polluted rivers and lakes through a process that couples high-alkali precipitation initiation with rhizosphere microecological activation; it also significantly promotes root development of emergent plants (mainly Iris tectorum), resulting in a denser and more abundant root network that forms a tightly integrated composite structure with the modified zeolite packing; furthermore, the production of plant root exudates is significantly increased, promoting the material exchange capacity of the rhizosphere environment and the activation level of insoluble phosphorus, further enhancing the overall phosphorus removal stability and long-term operational performance of the system; simultaneously, the anti-biofouling properties of the modified packing surface inhibit excessive biofilm accumulation, protect the active sites of the packing, and extend the system's operational lifespan. Attached Figure Description

[0017] Figure 1 These are elevation views and schematic diagrams of the filler-level structure of the constructed wetland system in the embodiments and comparative examples of the present invention; Figure 2 These are diagrams showing the changes in key water quality indicators and plant growth in an artificial wetland system as simulated in the embodiments and comparative examples of this invention. Figure 3 This is a graph showing the contribution of plants to phosphorus removal in the embodiments and comparative examples of the present invention; Figure 4 This is a comparative analysis chart of extracellular polymeric substances (EPS) in constructed wetlands of the present invention embodiments and comparative examples; Figure 5 This is a diagram of the phosphorus removal pathway in the artificial wetland of this invention. Detailed Implementation

[0018] The specific technical solution of the present invention will be further described in detail below with reference to specific examples.

[0019] As shown in the figure, an artificial wetland environment (vertical flow artificial wetland reactor) was simulated in the laboratory. The material used was plexiglass, the diameter of its vertical section was 0.20 meters, the height was 0.70 meters, and the height of the internal packing was 0.6 meters.

[0020] The constructed wetland is filled with LCZ-C (vertical flow constructed wetland reactor) packing material, with a packing height of 0.6 meters; from bottom to top, it is laid with a gravel support layer, an LCZ-C modified zeolite packing layer and a fine sand covering layer. The gravel support layer consists of two layers: the bottom layer has a particle size of 20 to 30 mm and a filling height of 0.08 to 0.15 m, and the top layer has a particle size of 5 to 10 mm and a filling height of 0.03 to 0.08 m. The particle size of the modified zeolite filler layer is set to 5 to 8 mm and the filling height is 0.2 to 0.5 m; The fine sand cover layer has a filling height of 0.1 to 0.2 meters. The constructed wetland system has an outlet every 15 centimeters along the height direction to collect samples from different layers.

[0021] A natural zeolite wetland was set up as a control. The artificial wetland shell of the natural zeolite wetland was the same as that in this embodiment. In the natural zeolite wetland, the gravel support layer was divided into two layers: the bottom layer had a particle size of 20 to 30 mm and a filling height of 0.08 to 0.15 m, and the upper layer had a particle size of 5 to 10 mm and a filling height of 0.03 to 0.08 m; the natural zeolite filler layer had a particle size of 5 to 8 mm and a filling height of 0.2 to 0.5 m; and the fine sand cover layer had a filling height of 0.1 to 0.2 m.

[0022] In both the examples and comparative examples, the constructed wetland systems were started up using activated sludge inoculation. Approximately 1000 mL of activated sludge was inoculated into each reactor and allowed to stand for 48 hours to complete initial acclimatization. Subsequently, culture medium was added to the reactor and aeration was carried out for 72 hours. Starting from the 4th day, slightly polluted river and lake water was continuously introduced for operation with a hydraulic retention time of 3 days.

[0023] During system operation, the total nitrogen (TN), total phosphorus (TP), and pH of the influent and effluent are continuously monitored.

[0024] In the initial stage of operation, the modified zeolite packing will release alkaline substances to maintain a high alkalinity environment in the water, generating insoluble precipitates such as hydroxyapatite (Ca5(PO4)3OH) and LaPO4, thereby removing phosphorus from the water.

[0025] Once the effluent pH drops from its initial high alkalinity to a stable range of 6.5 to 8.5, the plant colonization step begins. In this step, the system is maintained in stable operation within the specified pH range for 24 to 72 days. Then, yellow iris is colonized on the wetland surface at a predetermined density, ensuring that the selected plants have essentially the same biomass and that the weight difference between individual plants is less than 5 grams and the height difference is less than 0.5 centimeters. After colonization, the original operating conditions are maintained, and the water quality of the system's influent and effluent is continuously monitored.

[0026] During operation, the growth status of the plants and the phosphorus content of each part were measured; at the same time, extracellular polymeric substances (EPS) were extracted from the matrix surface, and the protein content in the EPS was determined using a BCA kit to verify the anti-biofouling performance of the modified filler.

[0027] Through the detailed structural parameters and operational control described above, the total phosphorus concentration in the effluent of this embodiment can be stably controlled at a low level, meeting the purification needs of urban micro-polluted rivers and lakes.

[0028] In summary, the features of this invention are: 1. By constructing a vertical flow constructed wetland reactor with a specific gradation and a high-alkali phosphorus fixation start-up stage, the removal efficiency of total phosphorus in slightly polluted rivers and lakes is significantly improved; in the system of this invention embodiment, under the condition that the influent total phosphorus concentration is 0.09-0.36 mg / L, the effluent total phosphorus concentration is stable between 0.001-0.06 mg / L, the average effluent concentration is 0.025 mg / L, the total phosphorus removal rate is stable at 87.41%, and the effluent concentration is maintained at approximately 0.022 mg / L in the later stage of operation. 1. The phosphorus removal efficiency is mg / L, demonstrating good deep purification ability and phosphorus removal stability, easily meeting surface water environmental quality standards; 2. In the initial stage of operation, the pH of the effluent from the system of this embodiment is approximately 11.5, which gradually decreases and stabilizes at approximately 8.5 over time; this process achieves phased control of phosphorus removal in constructed wetlands; the high pH stage completes the initial rapid fixation of phosphorus, and after the pH stabilizes, it enters the continuous operation stage with plant synergy, where the modified zeolite packing material continuously participates in phosphorus fixation; 3. The phased water quality regulation and the planting of emergent plants (mainly Iris tectorum) help improve the overall phosphorus removal stability and plant growth of the system; under the same operating conditions, compared with systems using natural zeolite packing material, the system of this embodiment exhibits better phosphorus removal efficiency. The biomass of aquatic plant roots is significantly increased, the contact between roots and the packing material is more thorough, and the accumulation of phosphorus in the plants is higher. Phosphorus can be further removed from the system through periodic harvesting of the above-ground parts, achieving resource utilization of phosphorus. 4. The total amount of plant root exudates (including organic acids such as succinic acid, lactic acid, fumaric acid, propionic acid, butyric acid, citric acid, and oxalic acid) is approximately 2.74 times that of the comparative example, promoting the material exchange capacity of the rhizosphere environment and the activation level of insoluble phosphorus, thus effectively maintaining the surface activity of the packing material. 5. The lanthanum chitosan-modified zeolite packing material used in this invention has excellent anti-biofouling properties. Compared with natural zeolite, the amount of bacteria attached to the surface of this packing material is reduced by more than 6 orders of magnitude, the amount of biofilm formation is significantly reduced, and the content of extracellular polymeric proteins on the matrix surface is reduced from 28.52%. The concentration of biofilm in the substrate was reduced from mg / Kg to 11.35 mg / Kg, effectively alleviating the substrate clogging problem caused by excessive biofilm accumulation in traditional constructed wetlands; 6. By inhibiting the occupation of active sites on the surface of the packing material by the biofilm, this invention ensures the long-term effectiveness of the substrate adsorption and phosphorus removal function, significantly extends the operating cycle of the constructed wetland system, and reduces the frequency of packing material replacement and operation and maintenance costs.

Claims

1. A long-term phosphorus removal method of anti-pollution and rhizosphere activation coupling wetland, characterized in that, Includes the following steps: Step (1) Construct a vertical flow constructed wetland reactor; Step (2) involves high-alkali phosphorus fixation treatment; Step (3) Adjust water quality and plant planting; Step (4) completes in-situ activation and synergistic phosphorus removal in the rhizosphere; Step (5) Maintain long-term stable operation of the system.

2. The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activated coupled wetland according to claim 1, characterized in that, The vertical flow constructed wetland reactor constructed in step (1) is cylindrical in shape and made of plexiglass; its height is 0.70 meters, its diameter is 0.20 meters, and the height of the internal packing is 0.6 meters. The vertical flow constructed wetland reactor is laid from bottom to top with a gravel support layer, a modified zeolite packing layer and a fine sand covering layer. The gravel support layer, the modified zeolite packing layer and the fine sand covering layer are filled with gravel, lanthanum chitosan modified zeolite packing and fine sand respectively.

3. The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activated coupled wetland according to claim 2, characterized in that, The gravel support layer consists of two layers: the bottom layer has a particle size of 20 to 30 mm and a filling height of 0.08 to 0.15 m, and the top layer has a particle size of 5 to 10 mm and a filling height of 0.03 to 0.08 m. The particle size of the modified zeolite filler layer is set to 5 to 8 mm and the filling height is 0.2 to 0.5 m; The filling height of the fine sand covering layer is 0.1 to 0.2 meters.

4. The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activated coupled wetland according to claim 2, characterized in that, The lanthanum-chitosan-modified zeolite filler is prepared by mixing and granulating a lanthanum-chitosan-zeolite composite material with cement, with a particle size of 5 to 8 mm and a cement mass fraction of 50%. The lanthanum-chitosan-modified zeolite filler has anti-biofouling properties. Through the electrostatic interaction between the positively charged groups of chitosan quaternary ammonium salt and the bacterial cell membrane, and the mechanical stress effect of the surface nanostructure formed by lanthanum loading on microorganisms, bacterial attachment and extracellular polymer secretion are synergistically inhibited, thereby alleviating matrix biofouling and protecting the active sites on the filler surface.

5. The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activated coupled wetland according to claim 1, characterized in that, The high-alkali phosphorus fixation treatment described in step (2) involves continuously introducing slightly polluted river and lake water into the reactor, using modified zeolite packing to initially release alkaline substances to maintain a high-alkalinity environment in the water, and fixing phosphorus in the water through chemical precipitation mediated by metal ions.

6. The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activated coupled wetland according to claim 5, characterized in that, In the high-alkali phosphorus fixation treatment, the pH of the water body is maintained between 11.0 and 12.0 in the initial stage of use of the modified zeolite packing, generating insoluble precipitates of hydroxyapatite and lanthanum phosphate.

7. The long-term phosphorus removal method of pollution-resistant and rhizosphere-activated coupled wetland according to claim 1, characterized in that, The water quality control and plant planting mentioned in step (3) are as follows: continuously monitor the pH of the effluent, and after the pH of the effluent drops to a normal range suitable for plant growth, plant artificial wetland emergent plants in the predetermined area of ​​the reactor. The emergent plants in the artificial wetland are selected from one or more combinations of yellow iris, reed, cattail, canna, umbrella sedge and loosestrife; In addition, the emergent plants in the artificial wetland must be at the same growth stage and grow uniformly, with the biomass deviation between plants controlled within 10%.

8. The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activated coupled wetland according to claim 1, characterized in that, The process of completing in-situ rhizosphere activation and synergistic phosphorus removal in step (4) involves using the low phosphorus stress environment created by the depletion of phosphorus in the water body due to high alkali fixation in the early stage to induce the spontaneous secretion of organic acids by the roots of emergent plants in the artificial wetland, neutralizing residual alkaline substances in the system and dissolving insoluble phosphorus on the surface of the packing material, thereby regenerating the active sites on the surface of the packing material. 9.The long-term phosphorus removal method of the pollution-resistant and rhizosphere-activation coupled wetland according to claim 8, characterized in that, The organic acids secreted by the roots of the emergent plants in the artificial wetland are at least one of succinic acid, lactic acid, fumaric acid, propionic acid, butyric acid, citric acid, and oxalic acid.

10. The long-term phosphorus removal method of pollution-resistant and rhizosphere-activated coupled wetland according to claim 1, characterized in that, The long-term stable operation of the system mentioned in step (5) is achieved by utilizing the positively charged microenvironment of chitosan quaternary ammonium salt on the surface of the modified zeolite filler and the mechanical / electrostatic synergistic antibacterial mechanism of lanthanum-loaded nanostructures to continuously inhibit excessive adhesion of microorganisms and secretion of extracellular polymers on the matrix surface, thereby preventing bio-blockage and occupation of active sites.

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