Method for removing phosphorus pollution in water body by using duckweed

Abstract

The invention provides a method for removing phosphorus pollution in a water body by using duckweed, and relates to the field of aquatic plant culture and low-phosphorus pollution water purification, and the method comprises the step of planting duckweed in a low endogenous phosphate state on the surface of the polluted water body. The method provided by the invention can continuously, stably and efficiently remove phosphate at a low concentration level in the polluted water body, and also can efficiently remove ammonia nitrogen in the water body, so that the quality of the effluent reaches the I-class water standard of surface water; according to the method, phosphorus and nitrogen in the water body are efficiently removed, fixation of carbon dioxide in air is improved, and the effect of continuously recycling carbon, phosphorus and nitrogen elements is achieved; meanwhile, the duckweed can rapidly grow and accumulate starch and protein, and the harvested duckweed biomass can be further recycled. According to the method, a closed-loop system of polluted water treatment, resource recovery and high-quality biomass production is constructed, and a green and efficient solution is provided for removing low-concentration phosphate in water.

Description

Technical Field

[0001] The present application relates to the technical field of aquatic plant cultivation and low-phosphorus contaminated water purification, and in particular to a method for removing phosphorus pollution in water bodies by utilizing duckweed. Background Art

[0002] Phosphorus is the primary controlling factor in the eutrophication process caused by nitrogen and phosphorus pollution in water bodies. Soluble phosphates in water bodies, as active phosphorus directly absorbed by organisms and algae, are the core driver of algal blooms. Studies have shown that when total phosphorus in surface water exceeds the threshold of 0.05 mg / L and phosphorus in the form of phosphate exceeds 0.025 mg / L, there is a risk of algal blooms. Furthermore, as phosphate concentrations decrease, treatment costs increase exponentially, reaching a treatment cost of $44.04 per pound to achieve an effluent phosphorus concentration below 0.05 mg / L. Existing phosphorus removal technologies face the following major bottlenecks when addressing low-concentration phosphorus pollution in water bodies (P < 0.5 mg / L): Among physical methods, membrane separation technology can achieve selective phosphate enrichment, but the treatment flux loss caused by membrane fouling and high costs restrict its large-scale application. Adsorption materials generally suffer from poor selectivity in the presence of multiple ions and insufficient regeneration cycle stability. Among chemical methods, chemical coagulation can only be used to remove high-concentration phosphates, while low-concentration phosphate removal is difficult to achieve due to the problem of agent dissolution balance. Among biological methods, the biofilm method is limited by the inhibition of microbial activity caused by the lack of carbon sources in the water, and is susceptible to biosafety issues such as phage invasion. Although artificial wetlands have advantages such as low technical maintenance and low energy consumption, the disadvantages are that some plants have low added value and low recycling rate. In addition, the release of endogenous phosphates in sediments further exacerbates the eutrophication process of water bodies, making it necessary to take into account the dual goals of removal and recovery in surface water phosphorus management to achieve long-term ecological regulation.

[0003] Duckweed is the smallest flowering plant in the world, with a total of 5 genera and 37 species. It is widely distributed in the world and has strong adaptability to the environment. It can grow in water temperatures above 5°C. It has nearly exponential growth characteristics, and its biomass can double in 30 hours under suitable conditions. Duckweed floats on the water surface, and the biomass and enriched nutrients can be recovered from the water body by directly salvaging. The salvaged duckweed can be directly used as livestock feed and fish bait. Patent No. 201810028570.X discloses a method for using high-quality light sources to promote the rapid purification of slightly polluted surface water by duckweed, and discloses the use of duckweed to remove nitrogen and phosphorus from surface water. However, this method also has limitations. Its processing volume is small (500mL) and the processing time is long, which is not conducive to resource recovery and large-scale application. Summary of the Invention

[0004] In view of this, the purpose of the present application is to provide a method for removing phosphorus pollution in water bodies by using duckweed, so as to solve the problems in the prior art that it is difficult to remove phosphate pollution at low concentration levels in water and it is not conducive to continuous resource recycling. The technical solution adopted by the present application to solve the above technical problems is as follows:

[0005] An embodiment of the present invention provides a method for removing phosphorus pollution in water bodies by using duckweed, including the following steps: planting duckweed in a low endogenous phosphate state on the surface of the polluted water body.

[0006] In some embodiments, in the duckweed in the low endogenous phosphate state, calculated by the fresh weight of the duckweed, PO3--P in the duckweed ≤ 0.5 mg / g; and / or

[0007] the types of the duckweed in the low endogenous phosphate state include one or more of Spirodela polyrhiza 8410, Spirodela oligorrhiza 0202, Azolla filiculoides DWC132, Azolla filiculoides 8695, Azolla filiculoides 0258; and / or

[0008] the coverage rate of the duckweed on the surface of the polluted water body is 100% - 130%.

[0009] In some embodiments, the polluted water body is the polluted water body in a continuous flow treatment tank.

[0010] In some embodiments, the continuous flow treatment tank is in a continuous flow mode of bottom inlet and top outlet, the flow rate of the continuous flow is V, and the depth of the continuous flow is H; and / or

[0011] the removal rate of PO43--P in the effluent of the continuous flow is P1; and / or

[0012] the removal rate of ammonia nitrogen in the effluent of the continuous flow is P2.

[0013] In some embodiments, V < 40 mL / min; and / or

[0014] H < 60 cm; and / or

[0015] the effluent volume of the continuous flow is < 384 L / m 2 / d; and / or

[0016] 70% < P1 < 98.20%; and / or

[0017] 80% < P2 < 94.46%.

[0018] In some embodiments, collecting the duckweed after removing phosphorus pollution in the water body, the biomass yield of the duckweed is M1, the starch content is M2, the starch yield is M3, the protein content is M4, the protein yield is M5, the phosphate recovery rate is M6, the total nitrogen recovery rate is M7, and the carbon fixation rate is M8; and / or

[0019] The phosphorus concentration range of the polluted water body is C1, and the ammonia nitrogen concentration range is C2.

[0020] In some embodiments, M1 is 2.28 g / m 2 / d to 10.69 g / m 2 / d; and / or

[0021] M2 is 1.23% to 25.30%; and / or

[0022] M3 is 0.038 g / m 2 / d to 2.42 g / m 2 / d; and / or

[0023] M4 is 14.74% to 28.02%; and / or

[0024] M5 is 0.67 g / m 2 / d to 2.34 g / m 2 / d; and / or

[0025] M6 is 13.99 mg / m 2 / d to 40.11 mg / m 2 / d; and / or

[0026] M7 is 107.78 mg / m 2 / d to 374.47 mg / m 2 / d; and / or

[0027] M8 is 0.92 g / m 2 / d to 4.30 g / m 2 / d; and / or

[0028] C1 < 0.5 mg / L; and / or

[0029] C2 < 2.5 mg / L.

[0030] In some embodiments, duckweed in a low-endogenous phosphate state is planted on the surface of the polluted water body and then cultured under light conditions, and the light conditions are one or more of red light, blue light, green light, and white light.

[0031] In some embodiments, the red light is provided by a red light LED lamp, with a peak wavelength of 660 nm, a full width at half maximum of 15 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s; and / or

[0032] The blue light is provided by a blue light LED lamp, with a peak wavelength of 450 nm, a full width at half maximum of 20 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s; and / or

[0033] The green light is provided by a green LED lamp, with a peak wavelength of 520 nm, a full width at half maximum of 15 nm, and a photosynthetic photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s; and / or

[0034] The white light is provided by a white LED lamp, with a photosynthetic photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s.

[0035] In some embodiments, the light illumination conditions are red light and white light, and the proportion of the red light is 30% to 90%, with the balance being white light.

[0036] In this application, phosphate-P is PO43--P.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] This application provides a continuous flow treatment method for the problem of difficult phosphorus removal in low-phosphate polluted water bodies, which can efficiently remove phosphorus and operate effectively for a long time. When the continuous water output reaches 333.12 L / m 2 / d, the removal rate of PO43--P in the effluent can be stably maintained above 90%, up to 98.20%; the removal rate of ammonia nitrogen in the effluent can be stably maintained above 90%, up to 94.46%. The concentrations of nitrogen and phosphorus in the effluent can be stabilized at about the Class I water standard specified in the "Surface Water Environment Quality Standard" (GB3838-2002). Compared with other phosphorus removal methods for low-phosphate water bodies, the present invention has the advantages of being fast, efficient, and stable;

[0039] While continuously removing nitrogen and phosphorus from the water body, this application also has the advantages of continuous recovery of phosphorus, nitrogen, and carbon, as well as continuous production of duckweed biomass, starch, and protein. The method of the present invention uses the technologies of continuous flow and 90% red light, so that the average phosphate recovery rate is 31.00 mg / m 2 / d, and the highest phosphate recovery rate is 40.11 mg / m 2 / d. The average total nitrogen recovery rate is 297.70 mg / m 2 / d, and the highest total nitrogen recovery rate is 374.47 mg / m 2 / d. The average carbon fixation rate is 3.31 g / m 2 / d, and the highest carbon fixation rate is 4.30 g / m 2 / d. The average duckweed biomass production reaches 8.49 g / m 2 / d, the highest biomass yield reaches 10.69 g / m 2 / d. The average starch content reaches 14.94%, and the highest starch content reaches 25.30%. The average starch yield is 1.28 g / m 2 / d, and the highest starch yield is 2.42 g / m 2 / d. The average protein content is 22.22%, and the highest protein content is 28.02%. The average protein yield is 1.86 g / m 2 / d, and the highest protein yield is 2.34 g / m 2 / d;

[0040] While solving the problems of efficient phosphorus removal from low-phosphate water bodies and improving the starch and protein production capabilities of duckweed, this application also has the advantage of reducing power consumption. Under the illumination conditions of the same photon flux density, using 90% red light saves 18.39% of electric energy compared to white light;

[0041] The method for removing low phosphate from water bodies described in this application is simple to operate, low in cost, and easy to promote and apply; the method of using duckweed to simultaneously absorb nitrogen and phosphorus in water bodies and carbon dioxide in the air and produce starch and protein has the advantages of being green, environmentally friendly, recyclable, and having high added value. Brief Description of the Drawings

[0042] In order to more clearly illustrate the technical solutions of the embodiments of this application, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of this application and do not limit this application, where:

[0043] Figure 1 is a comparison diagram of the phosphate removal effects of different varieties of duckweed in Class V water in Comparative Example 1 and Example 1;

[0044] Figure 2 is a comparison diagram of the phosphate removal effects of different initial phosphate contents of duckweed in Class V water, as well as the phosphate absorption-related genes and ATP enzyme activities in Comparative Example 2 and Example 2;

[0045] Figure 3 is a comparison diagram of the phosphate removal effects of duckweed in Class V water under different spectra in Comparative Example 3 and Example 3;

[0046] Figure 4 is a comparison diagram of the biomass yield and growth rate, starch content and growth rate, and starch yield and growth rate of duckweed under different spectra in Comparative Example 3 and Example 3;

[0047] Figure 5 is a comparison diagram of the phosphate removal effects of duckweed in Class V water under different red light ratios in Comparative Example 3 and Example 4;

[0048] Figure 6 It is a comparison chart of duckweed biomass yield, yield increase rate, starch yield and yield increase rate under different red light ratios in Comparative Example 3 and Example 4;

[0049] Figure 7 It is a comparison chart of the phosphate removal effect and phosphate recovery flux of static and continuous-flow duckweed in different depths of Class V water in Comparative Example 4 and Example 5;

[0050] Figure 8 It is a comparison chart of the phosphate removal effect of duckweed in Class V water under different light qualities and continuous-flow conditions in Comparative Example 5 and Example 6;

[0051] Figure 9 It is a comparison chart of the ammonia nitrogen removal effect of duckweed in Class V water under different light qualities and continuous-flow conditions in Comparative Example 5 and Example 6;

[0052] Figure 10 It is a comparison chart of duckweed biomass yield, starch and protein contents, starch and protein yields under different light qualities and continuous-flow conditions in Comparative Example 5 and Example 6;

[0053] Figure 11 It is a comparison chart of phosphate recovery, total nitrogen recovery, and carbon fixation rate of duckweed under different light qualities and continuous-flow conditions in Comparative Example 5 and Example 6. Detailed implementation manners

[0054] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation manners described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0055] In the present application, unless otherwise stated, the orientation words such as "upper" and "lower" usually refer to the upper and lower in the actual use or working state of the device; in addition, in the description of the present application, the term "including" means "including but not limited to".

[0056] In the present application, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural.

[0057] In this application, "at least one" means one or more, and "a plurality" means two or more. "One or several", "at least one (item)" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one (item) of a, b, or c", or "at least one (item) of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0058] The various embodiments of this application can exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub - ranges and individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub - ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0059] In a first aspect, an embodiment of the present invention provides a method for removing phosphorus pollution in water bodies using duckweed, comprising the following steps: planting duckweed in a low - endogenous phosphate state on the surface of the polluted water body.

[0060] The ATP enzyme activity of the duckweed in a low - endogenous phosphate state in this application and the gene expression levels related to phosphate absorption are significantly increased, which is beneficial to the active absorption of low - concentration phosphate in the water body by duckweed.

[0061] The method of this application can continuously, stably, and efficiently remove low - concentration phosphate in the polluted water body, and can also efficiently remove ammonia nitrogen in the water body. The effluent quality reaches the standard of surface water class I. This application not only efficiently removes phosphorus and nitrogen in the water body, but also improves the fixation of carbon dioxide in the air, achieving the effect of continuous recycling of carbon, phosphorus, and nitrogen elements. At the same time, the duckweed in this application can grow rapidly and accumulate starch and protein, and the harvested duckweed biomass can be further utilized for resource recovery.

[0062] This application constructs a closed-loop system for treating polluted water bodies - resource recovery - high-quality biomass production, providing a green and efficient solution for removing low-concentration phosphate in water. In some embodiments, in the duckweed with a low endogenous phosphate state, calculated based on the fresh weight of the duckweed, the PO43--P in the duckweed is ≤ 0.5 mg / g, for example, it can be: 0.05 mg / g, 0.1 mg / g, 0.15 mg / g, 0.17 mg / g, 0.2 mg / g, 0.22 mg / g, 0.25 mg / g, 0.28 mg / g, 0.3 mg / g, 0.32 mg / g, 0.35 mg / g, 0.38 mg / g, 0.4 mg / g, 0.42 mg / g, 0.45 mg / g, 0.48 mg / g, 0.5 mg / g, etc.

[0063] In some embodiments, the types of duckweed with a low endogenous phosphate state include one or more of Spirodela polyrhiza 8410, Spirodela oligorrhiza 0202, Azolla filiculoides DWC132, Azolla filiculoides 8695, Azolla filiculoides 0258.

[0064] In some embodiments, the polluted water body is the polluted water body in a continuous flow treatment tank.

[0065] Furthermore, the continuous flow treatment tank is in a continuous flow mode of bottom-in and top-out.

[0066] Even further, the flow rate of the continuous flow is V.

[0067] Even further, the depth of the continuous flow is H.

[0068] Even further, V < 40 mL / min, for example, it can be 1 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 39 mL / min, etc.

[0069] Even further, H < 60 cm, for example, it can be 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, 50 cm, 55 cm, 59 cm. Within the range of the flow rate and depth, the low-concentration phosphate in the polluted water body can be well removed.

[0070] Furthermore, the water output of the continuous flow is < 384 L / m 2 / d, for example, it can be 10 L / m 2 / d, 50 L / m 2 / d, 100 L / m 2 / d, 150 L / m 2 / d, 200 L / m 2 / d, 250 L / m 2 / d, 300 L / m 2 / d, 350 L / m 2 / d, 384 L / m 2 / d, etc.

[0071] Furthermore, the removal rate of PO43--P in the effluent of the continuous flow is P1.

[0072] Even further, 70% < P1 < 98.20%, for example, P1 can be 71%, 75%, 78%, 80%, 82%, 85%, 88%, 92%, 93%, 94%, 95%, 96%, 97%, 97.65%, 98.10%, etc.

[0073] Furthermore, the removal rate of ammonia nitrogen in the effluent of the continuous flow is P2.

[0074] Even further, 80% < P2 < 94.46%, for example, P1 can be 81%, 85%, 88%, 90%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.4%, etc.

[0075] In some embodiments, the duckweed after removing the phosphorus pollution in the water body is collected. The duckweed biomass yield is M1, the starch content is M2, the starch yield is M3, the protein content is M4, the protein yield is M5, the phosphate recovery rate is M6, and the total nitrogen recovery rate is M7, and the carbon fixation rate is M8.

[0076] Furthermore, M1 is 2.28 g / m 2 / d to 10.69 g / m 2 / d, for example, it can be 2.28 g / m 2 / d, 2.5 g / m 2 / d, 3 g / m 2 / d, 3.5 g / m 2 / d, 4 g / m 2 / d, 4.5 g / m 2 / d, 5 g / m 2 / d, 5.5 g / m 2 / d, 6 g / m 2 / d, 6.5 g / m 2 / d, 7 g / m 2 / d, 7.5 g / m 2 / d, 8 g / m 2 / d, 8.5 g / m 2 / d, 9 g / m 2 / d, 9.5 g / m 2 / d, 9.7 g / m 2 / d, 10 g / m 2 / d, 10.2 g / m2 / d, 10.69 g / m 2 / d.

[0077] Furthermore, M2 is 1.23% to 25.30%, and can be, for example, 1.23%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 21%, 22%, 22.5%, 24%, 25.30%, etc.

[0078] Furthermore, M3 is 0.038 g / m 2 / d to 2.42 g / m 2 / d, and can be, for example, 0.038 g / m 2 / d, 0.05 g / m 2 / d, 0.08 g / m 2 / d, 0.1 g / m 2 / d, 0.8 g / m 2 / d, 1.2 g / m 2 / d, 1.8 g / m 2 / d, 2 g / m 2 / d, 2.1 g / m 2 / d, 2.2 g / m 2 / d, 2.3 g / m 2 / d, 2.42 g / m 2 / d.

[0079] Furthermore, M4 is 14.74% to 28.02%, and can be, for example, 14.74%, 15%, 18%, 20%, 22%, 24%, 26%, 28.02%, etc.

[0080] Furthermore, M5 is 0.67 g / m 2 / d to 2.34 g / m 2 / d, and can be, for example, 0.67 g / m 2 / d, 1 g / m 2 / d, 1.2 g / m 2 / d, 1.5 g / m 2 / d, 1.8 g / m 2 / d, 2 g / m 2 / d, 2.1 g / m 2 / d, 2.2 g / m 2 / d, 2.3 g / m 2 / d, 2.34 g / m 2 / d, etc.

[0081] Furthermore, M6 is 13.99 mg / m 2 / d to 40.11 mg / m 2 / d, and can be, for example, 13.99 mg / m2 / d, 18 mg / m 2 / d, 20 mg / m 2 / d, 25 mg / m 2 / d, 30 mg / m 2 / d, 35 mg / m 2 / d, 40 mg / m 2 / d, 40.11 mg / m 2 / d etc.

[0082] Furthermore, M7 is 107.78 mg / m 2 / d to 374.47 mg / m 2 / d, for example, it can be 107.78 mg / m 2 / d, 120 mg / m 2 / d, 180 mg / m 2 / d, 200 mg / m 2 / d, 250 mg / m 2 / d, 300 mg / m 2 / d, 320 mg / m 2 / d, 350 mg / m 2 / d, 360 mg / m 2 / d, 374.47 mg / m 2 / d etc.

[0083] Furthermore, M8 is 0.92 g / m 2 / d to 4.30 g / m 2 / d, for example, it can be 0.92 g / m 2 / d, 1.2 g / m 2 / d, 1.8 g / m 2 / d, 2 g / m 2 / d, 2.8 g / m 2 / d, 3 g / m 2 / d, 3.5 g / m 2 / d, 3.8 g / m 2 / d, 4 g / m 2 / d, 4.2 g / m 2 / d, 4.3 g / m 2 / d.

[0084] Exemplarily, the polluted water body is the polluted water body of a continuous flow treatment tank. The continuous flow treatment tank is a container with a depth of 50 cm and a surface area of 0.15 m 2 The continuous flow mode has an inlet height of 2 cm and an outlet height of 50 cm. The flow rate of the continuous flow is V = 34.7 mL / min, and the depth of the continuous flow is H = 50 cm.

[0085] In some embodiments, the polluted water body is the polluted water body in the static treatment tank.

[0086] In some embodiments, duckweed in a low endogenous phosphate state is planted on the surface of the polluted water body and then cultured under light conditions.

[0087] Furthermore, the light conditions are one or more of red light, blue light, green light, and white light.

[0088] Still further, the red light is provided by a red light LED lamp, with a peak wavelength of 660 nm, a full width at half maximum of 15 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s, for example, it can be 110 μmol / m 2 / s, 115 μmol / m 2 / s, 120 μmol / m 2 / s, 125 μmol / m 2 / s, 130 μmol / m 2 / s, etc.

[0089] Still further, the blue light is provided by a blue light LED lamp, with a peak wavelength of 450 nm, a full width at half maximum of 20 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s, for example, it can be 110 μmol / m 2 / s, 115 μmol / m 2 / s, 120 μmol / m 2 / s, 125 μmol / m 2 / s, 130 μmol / m 2 / s, etc.

[0090] Still further, the green light is provided by a green light LED lamp, with a peak wavelength of 520 nm, a full width at half maximum of 15 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s, for example, it can be 110 μmol / m 2 / s, 115 μmol / m 2 / s, 120 μmol / m 2 / s, 125 μmol / m 2 / s, 130 μmol / m 2 / s, etc.

[0091] Still further, the white light is provided by a white light LED lamp, with a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s, for example, it can be 110 μmol / m 2 / s, 115 μmol / m 2 / s, 120 μmol / m 2 / s, 125 μmol / m 2 / s, 130 μmol / m 2 / s, etc.

[0092] Furthermore, the light condition is red light and white light, and the proportion of the red light is 30% - 90%, for example, it can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., and the balance is white light.

[0093] In some embodiments, the phosphorus concentration range of the polluted water body is C1, and the ammonia nitrogen concentration range is C2.

[0094] Furthermore, C1 < 0.5 mg / L, for example, it can be 0.05 mg / L, 0.1 mg / L, 0.15 mg / L, 0.2 mg / L, 0.25 mg / L, 0.3 mg / L, 0.35 mg / L, 0.4 mg / L, 0.45 mg / L, 0.49 mg / L, etc.

[0095] Furthermore, C2 < 2.5 mg / L, for example, it can be 0.5 mg / L, 0.8 mg / L, 1 mg / L, 1.2 mg / L, 1.5 mg / L, 1.8 mg / L, 2 mg / L, 2.2 mg / L, 2.4 mg / L, etc.

[0096] In some embodiments, the coverage rate of duckweed on the surface of the polluted water body is 100% - 130%, for example, it can be 105%, 110%, 115%, 120%, 125%, 128%, 130%, etc.

[0097] It can be understood that during the process of duckweed removing low - concentration phosphate in water, part of the duckweed is salvaged every 1 day to ensure that the coverage rate of duckweed on the surface of the polluted water body is 100% - 130%.

[0098] It can also be understood that the polluted water body is surface water.

[0099] The following further illustrates the present invention with comparative examples and examples:

[0100] The duckweeds used in the present invention are Landoltia punctata 0202, Spirodela intermedia 8410, Lemna minor 8695, Lemna minor 0258, and Lemna gibba DWC132, all from the duckweed germplasm resource bank of the Chengdu Institute of Biology, Chinese Academy of Sciences (http: / / www.zfish.cn / meetingResource).

[0101] The following examples and comparative examples were carried out simultaneously. For the reagents and test equipment used in the examples and comparative examples, unless otherwise specified, they are all conventional reagents and experimental equipment.

[0102] 1. Determination and calculation methods for duckweed biomass-related indicators

[0103] For the determination of fresh weight, dry weight, phosphate content, starch content, protein content, total nitrogen, and total carbon content of duckweed in the examples and comparative examples, the analysis methods used are all conventional analysis methods.

[0104] Calculation of biomass static treatment:

[0105] Duckweed biomass yield (g / m 2 / d) = (dry weight of duckweed at sampling - dry weight of duckweed at the previous sampling) / sampling water surface area / culture time;

[0106] Duckweed biomass increase rate (%) = (biomass yield in the example - biomass yield in the comparative example) / biomass yield in the comparative example * 100%.

[0107] Calculation of biomass continuous flow treatment:

[0108] Duckweed biomass yield (g / m 2 / d) = dry weight of duckweed at sampling / sampling water surface area / culture time;

[0109] Calculation of starch content and yield:

[0110] Starch content = measured glucose content / 1.1;

[0111] Starch content increase rate (%) = (starch content of duckweed in the example - starch content of duckweed in the comparative example) / starch content of duckweed in the comparative example * 100%.

[0112] Starch yield (g / m 2 / d) = biomass yield of duckweed at sampling × starch content of duckweed at sampling;

[0113] Starch yield increase rate (%) = (Starch yield of duckweed in the example - Starch yield of duckweed in the control) / Starch yield of duckweed in the control * 100%.

[0114] Calculation of protein content and yield:

[0115] Protein content = Kjeldahl nitrogen content * 6.25;

[0116] Duckweed protein yield (g / m 2 / d) = Biomass yield of duckweed at sampling * Protein content of duckweed at sampling;

[0117] Calculation of phosphate, total nitrogen, and carbon fixation rate:

[0118] Duckweed phosphate recovery rate (mg / m 2 / d) = (Fresh weight at sampling * Phosphate content at sampling) / Sampling water surface area / Cultivation time;

[0119] Duckweed total nitrogen recovery rate (mg / m 2 / d) = Total nitrogen content of sampled duckweed * Biomass yield of duckweed at sampling;

[0120] Duckweed carbon fixation rate (g / m 2 / d) = Total carbon content of sampled duckweed * Biomass yield of duckweed at sampling.

[0121] 2. Preparation methods of various solutions

[0122] The preparation method of Hoagland culture solution is as follows: Six mother liquors A, B, C, D, E, and F are prepared with distilled water according to the concentrations of each reagent in the mother liquor formula described in the following table. Hoagland culture solution is prepared with distilled water according to the addition amount of each mother liquor in each liter of Hoagland culture solution described in the following table, and the pH value of Hoagland culture solution is adjusted to 5.0 by HCl and KOH. The prepared Hoagland culture solution is mixed evenly with distilled water four times its volume to obtain 1 / 5 Hoagland, and the pH value is adjusted to 5.0.

[0123] Table 1 Composition table of each mother liquor in Hoagland culture solution formula

[0124]

[0125] 3. Preparation of low-phosphate water body and determination of ammonia nitrogen and phosphate in water body

[0126] (1) Preparation of low-phosphate water body

[0127] In the examples and comparative examples, the low-phosphate water bodies were prepared by adding ammonium chloride and potassium dihydrogen phosphate to tap water according to the Class V water quality specified in the Environmental Quality Standards for Surface Water (GB3838-2002), so that the ammonia nitrogen and phosphate contents in the prepared water bodies reached the theoretical Class V surface water quality standards. The pH was adjusted to 7.0.

[0128] (2) Determination of ammonia nitrogen and phosphate in water bodies

[0129] The detection of phosphate content in water bodies was carried out according to the molybdenum-antimony anti-colorimetric method in the national standard HJ 632-2011; the detection of ammonia nitrogen-nitrogen was determined by the ammonia nitrogen detection kit Test 14752 produced by Merck KGaA, Germany, and the detection method was carried out according to the instructions.

[0130] 4. Light source conditions

[0131] The light sources of each comparative example were white LED lights. In each example, unless otherwise specified, red light was provided by a red LED light with a peak wavelength of 660 nm and a full width at half maximum of 15 nm, hereinafter referred to as red; blue light was provided by a blue LED light with a peak wavelength of 450 nm and a full width at half maximum of 20 nm, hereinafter referred to as blue. The peak wavelength of green light was 520 nm and the full width at half maximum was 15 nm, hereinafter referred to as green.

[0132] In the whole text, the ratio of each light is the ratio of photon flux density, and the photon flux density refers to the light density of the corresponding light source on the surface of duckweed.

[0133] The following examples and comparative examples were carried out synchronously.

[0134] Comparative Example 1: Removal of phosphate in Class V water by different varieties of duckweed in a high-phosphate state

[0135] (1) Each variety of duckweed was cultured in a nutrient solution with a PO43--P content of 31 mg / L and other nutrients prepared with 1 / 5 Hoagland nutrient solution for 4 days. In a culture container with a depth of 5 cm and a surface area of 118.8 cm 2 500 mL of Class V water was added, and 2.0 g of fresh duckweed (coverage rate of about 100%) was inoculated on the water surface. Under a white LED light at room temperature of 25 °C and a photon flux density of 110 μmol / m 2 / s, it was cultured under full light for 2 days, and the water was replenished to the original liquid level height with distilled water every day.

[0136] (2) At 0 hours, 6 hours, 1 day, and 2 days of cultivation, take duckweed samples. Wash the fresh duckweed 3 times with clear water, blot dry the water with absorbent paper, weigh 0.3 g of the fresh sample, and store it at -80 °C. The supernatant of the homogenized fresh duckweed sample was used to detect the phosphate content of duckweed according to the above method for measuring the phosphate content in water bodies. The results are shown in Table 2. The initial average PO43--P content of Spirodela polyrhiza 8410 was 0.77 mg / g fresh weight; that of Lemna aequinoctialis 0202 was 0.56 mg / g fresh weight; that of Azolla filiculoides DWC132 was 1.19 mg / g fresh weight; that of Azolla filiculoides 8695 was 1.15 mg / g fresh weight; and that of Azolla filiculoides 0258 was 1.44 mg / g fresh weight.

[0137] (3) At 0 hours, 6 hours, 1 day, and 2 days of cultivation, take water samples, measure the phosphate concentration of the water samples, and calculate the removal rate of phosphate by duckweed. The results of the average phosphate removal rate of duckweed at 6 hours are shown in Table 2. The phosphate removal rate of Spirodela polyrhiza 8410 was -11.15%; that of Lemna aequinoctialis 0202 was -41.09%; that of Azolla filiculoides DWC132 was -34.21%; that of Azolla filiculoides 8695 was -31.42%; and that of Azolla filiculoides 0258 was -101.88%. Continuously monitor the effect of duckweed on removing phosphate from water bodies as Figure 1 shown in A. When the initial phosphate content of duckweed is high, the effect of removing phosphate from water bodies is generally poor, and there is a phenomenon of releasing phosphate into the water body in the first 6 hours. Especially after treating the water body with Azolla filiculoides 0258 for 2 days, there is still phosphate residue in the water body, while other duckweeds can complete the treatment of phosphate in the water body at 2 days. This indicates that a high phosphate content in duckweed itself is not conducive to the removal of phosphate from water bodies.

[0138] Example 1: Different varieties of duckweed remove phosphate from Class V water in a low phosphate state

[0139] (1) Each variety of duckweed was cultivated in a nutrient solution with a PO43--P content of 0.31 mg / L and other nutrients prepared with reference to 1 / 5 Hoagland nutrient solution for 4 days to obtain duckweed in a low endogenous phosphate state. The duckweed in a low endogenous phosphate state was cultivated in Class V water according to the operation steps in Comparative Example 1. Sampling and measurement of water bodies and duckweed were all carried out as described in Comparative Example 1.

[0140] (2) The initial phosphate content results of duckweed are shown in Table 2. The initial average PO43--P content of Spirodela polyrhiza 8410 was 0.22 mg / g fresh weight; that of Lemna aequinoctialis 0202 was 0.23 mg / g fresh weight; that of Azolla filiculoides DWC132 was 0.21 mg / g fresh weight; that of Azolla filiculoides 8695 was 0.21 mg / g fresh weight; and that of Azolla filiculoides 0258 was 0.20 mg / g fresh weight.

[0141] (3) The results of the average phosphate removal rate of duckweed in 6 hours are shown in Table 2. The average phosphate removal rate of Spirodela polyrhiza 8410 is 45.55%; the average phosphate removal rate of Spirodela oligorrhiza 0202 is 27.14%; the average phosphate removal rate of Azolla filiculoides DWC132 is 78.64%; the average phosphate removal rate of Azolla filiculoides 8695 is 70.65%; the average phosphate removal rate of Azolla filiculoides 0258 is 83.66%. The continuous monitoring of the phosphate removal effect of duckweed on water body is as Figure 1 shown in Figure B. When the initial phosphate content of duckweed is low, the effect of removing phosphate from the water body is greatly improved compared with the state of high phosphate content of duckweed in Comparative Example 1. The order of phosphate removal effect is Azolla filiculoides > Spirodela polyrhiza > Spirodela oligorrhiza. Among the three types of Azolla filiculoides, Azolla filiculoides 0258 has the best removal effect.

[0142] Table 2 The effect of different varieties of duckweed on removing phosphate in Class V water under white light with different phosphate content states

[0143]

[0144] Comparative Example 2: Duckweed with high phosphate removal for removing phosphate in Class V water

[0145] (1) Azolla filiculoides 0258 was cultured in a nutrient solution with a PO43--P content of 31 mg / L and other nutrients prepared according to 1 / 5 Hoagland nutrient solution for 4 days to obtain duckweed with high phosphate content, abbreviated as HP. The Azolla filiculoides 0258 in the state of high phosphate content was cultured in Class V water according to the operation steps in Comparative Example 1. The operations such as water body and duckweed sampling and determination were carried out as described in Comparative Example 1.

[0146] (2) The results of the initial phosphate content of duckweed are shown in Table 3. The average initial PO43--P content of duckweed in the HP group is 1.00 mg / g fresh weight.

[0147] (3) The results of the average phosphate removal rate of duckweed in 6 hours are shown in Table 3. The average phosphate removal rate of HP is -56.06%. The continuous monitoring of the phosphate removal effect of duckweed on water body is as Figure 2 shown in Figure A. The duckweed in the HP group with a phosphate content state needs 2 days to finish treating the phosphate in Class V water.

[0148] Example 2: Duckweed with low phosphate state for removing phosphate in Class V water

[0149] (1) Duckweed 0258 was cultured in a nutrient solution with a PO43--P content of 6.20 mg / L, and other nutrients were prepared with reference to 1 / 5 Hoagland nutrient solution for 4 days to obtain duckweed with medium phosphate content, abbreviated as MP; Duckweed 0258 was cultured in a nutrient solution with a PO43--P content of 0.31 mg / L, and other nutrients were prepared with reference to 1 / 5 Hoagland nutrient solution for 4 days to obtain duckweed in a low endogenous phosphate state, abbreviated as LP. The duckweed 0258 in these two phosphate content states was cultured in type V water according to the operation steps in Comparative Example 1. Operations such as water body and duckweed sampling and determination were carried out as described in Comparative Example 1.

[0150] (2) The results of the initial phosphate content of duckweed are shown in Table 3. The average initial PO43--P content of duckweed in the MP group was 0.57 mg / g fresh weight; The average initial PO43--P content of duckweed in the LP group was 0.17 mg / g fresh weight.

[0151] (3) The results of the average phosphate removal rate of duckweed in 6 hours are shown in Table 3. MP was 48.79%; LP was 87.93%. These results indicate that the lower the initial phosphate content of duckweed, the better the phosphate removal effect. Continuously monitor the phosphate removal effect of duckweed on the water body as Figure 2 shown. LP duckweed can finish treating the phosphate in type V water in 1 day. The ability of duckweed to remove phosphate in the 2-day water treatment was LP > MP > HP. This indicates that the low phosphate content state of duckweed can significantly promote the phosphate removal ability of duckweed on the water body, and the lower the phosphate content of duckweed, the more obvious the removal effect.

[0152] (4) The mechanism analysis is as Figure 2 shown in Figures 2C and 2B. The expression levels of some genes related to phosphate absorption in the LP group of duckweed, namely PHT1;4, PHT1;8, VPT, and VPE, were all significantly higher than those in the MP and HP groups (P < 0.05). In addition, the PHT1;8 and VPE genes in the MP group were also significantly up-regulated compared to the HP group (P < 0.05). The increase in ATPase activity can promote the absorption of phosphate by plants. The ATPase activities of LP and MP groups of duckweed were 3.19 times and 2.11 times higher than that of the HP group, respectively. These all indicate that the lower the endogenous phosphorus content of duckweed, the stronger the activation of the mechanism for duckweed to actively absorb phosphate. Therefore, to achieve better phosphorus removal effect, duckweed with lower endogenous phosphate content should be used.

[0153] Table 3 Effect of different phosphate content states of duckweed 0258 on removing phosphate in type V water under white light

[0154]

[0155] Comparative Example 3: Phosphate removal from type V water by duckweed in a low phosphate state under white light

[0156] (1) Combining the phosphate removal effects of Example 1 and Example 2, when the phosphate content of Azolla 0258 is controlled at ≤ 0.2 mg / g fresh weight, this condition can be considered as Azolla being in a low phosphate state. The Azolla 0258 in the low phosphate state was cultured in a culture container with a depth of 5 cm and a surface area of 328.02 cm 2 1400 mL of Class V water was added to the container, and 5.0 g of fresh Azolla was inoculated on the water surface (coverage rate was about 100%). Other conditions were the same as those in Comparative Example 1. The operations such as water body and Azolla sampling and determination were carried out as described in Comparative Example 1.

[0157] (2) The Azolla in Comparative Example 3 was designated as White. The results of the average phosphate removal rate of Azolla in 6 hours are shown in Table 4. For White, it was 71.88%. The continuous monitoring of the phosphate removal effect of Azolla on the water body is as Figure 3 shown. Azolla can remove the phosphate in Class V water within 1 day. The biomass yield, starch content, and starch yield are as Figure 4 shown. The average values of the biomass yield, starch content, and starch yield are 0.54 g / m 2 / d, 9.31%, and 0.05 g / m 2 / d respectively. It can be seen that the biomass yield, starch content, and starch yield of Azolla under white light are all relatively low.

[0158] Example 3: Phosphate removal from Class V water by Azolla in the low phosphate state under different light qualities

[0159] (1) The Azolla 0258 in the state of low phosphate content was placed under red light, blue light, and green light respectively, and other conditions were exactly the same as those in Comparative Example 3. The operations such as water body and Azolla sampling and determination were carried out as described in Comparative Example 1.

[0160] (2) The Azolla placed under red light, blue light, and green light were designated as Red, Blue, and Green respectively. The results of the average phosphate removal rate of Azolla in 6 hours are shown in Table 4. For Red, it was 88.22%; for Blue, it was 87.86%; for Green, it was 80.96%. The average improvement rates of phosphate removal of Red, Blue, and Green compared with White were 22.73%, 22.22%, and 12.63% respectively. The continuous monitoring of the phosphate removal effect of Azolla on the water body is as Figure 3 shown. Azolla under all spectra can remove the phosphate in Class V water within 1 day. The biomass yield, starch content, and starch yield of Red, Blue, and Green are as Figure 4 shown. The average values of the biomass yield, starch content, and starch yield of Red are 10.24 g / m 2 / d, 39.91%, and 4.09 g / m 2 / d. The average increase rates of biomass yield, starch content, and starch yield of Red compared to White are 1811.61%, 328.63%, and 8087.14% respectively. The average values of biomass yield, starch content, and starch yield of Blue are 5.39 g / m 2 / d, 30.28%, 1.63 g / m 2 / d. The average increase rates of biomass yield, starch content, and starch yield of Blue compared to White are 905.90%, 225.21%, and 3170.07% respectively. The average values of biomass yield, starch content, and starch yield of Green are 1.46 g / m 2 / d, 6.34%, 0.09 g / m 2 / d. The average increase rates of biomass yield, starch content, and starch yield of Green compared to White are 171.79%, -31.91%, and 85.00% respectively. These results indicate that the ability of duckweed to remove phosphate, biomass yield, starch content, and starch yield are the best under red light. Blue light also has an enhancing effect on the ability to remove phosphate, biomass yield, starch content, and starch yield, but the overall effect is not as good as that of red light. Green light can improve the ability of duckweed to remove phosphate and biomass yield.

[0161] Table 4 Effect of Wolffia arrhiza 0258 on removing phosphate in Class V water under low phosphate conditions with different light qualities

[0162]

[0163] Example 4: Removal of phosphate in Class V water by duckweed under low phosphate conditions with different proportions of red light

[0164] (1) Since other light qualities can also promote the phosphate removal effect of duckweed. We tested the effect of increasing the proportion of red light on the phosphate removal and biomass yield improvement of duckweed. Wolffia arrhiza 0258 in the low phosphate content state was placed under 30% red light, 60% red light, and 90% red light respectively, and other conditions were exactly the same as those in Comparative Example 3. The operations of water body and duckweed sampling and determination were carried out as described in Comparative Example 1.

[0165] (2) The duckweed placed under 30% red light, 60% red light, and 90% red light are respectively designated as 30% Red, 60% Red, and 90% Red. The results of the average phosphate removal rate of duckweed in 6 hours are shown in Table 5. The phosphate removal rate of 30% Red is 65.17%; that of 60% Red is 74.79%; that of 90% Red is 89.13%. The average increase rates of phosphate removal of 30% Red, 60% Red, and 90% Red compared to White are -9.34%, 4.04%, and 23.99% respectively. Continuously monitor the effect of duckweed on phosphate removal from the water body as Figure 5As shown, duckweeds under 30% Red, 60% Red, and 90% Red can all finish treating phosphate in Class V water within 1 day. The biomass yield, starch content, and starch yield of 30% Red, 60% Red, and 90% Red are as Figure 6 shown. The average values of the biomass yield, starch content, and starch yield of 30% Red are 5.72 g / m 2 / d, 29.38%, and 1.68 g / m 2 / d respectively. The average increase rates of the biomass yield, starch content, and starch yield of 30% Red compared to White are 967.16%, 215.60%, and 3266.52% respectively. The average values of the biomass yield, starch content, and starch yield of 60% Red are 9.66 g / m 2 / d, 38.76%, and 3.74 g / m 2 / d respectively. The average increase rates of the biomass yield, starch content, and starch yield of 60% Red compared to White are 1704.02%, 316.27%, and 7402.35% respectively. The average values of the biomass yield, starch content, and starch yield of 90% Red are 10.39 g / m 2 / d, 39.27%, and 4.08 g / m 2 / d respectively. The average increase rates of the biomass yield, starch content, and starch yield of 90% Red compared to White are 1839.10%, 321.83%, and 8073.21% respectively. These results indicate that increasing the proportion of red light is beneficial to the biomass yield, starch content, and starch yield of duckweed. However, to increase the phosphate removal ability of duckweed, the proportion of red light should be at least above 60%. The test results show that the best proportion of red light for improving the phosphate removal ability and biomass yield of duckweed is 90%.

[0166] Table 5 Effect of Azolla imbricata 0258 in low phosphate state on removing phosphate in Class V water under different red light proportions

[0167]

[0168] Control Example 4: Phosphate removal by Azolla imbricata in low phosphate state under static conditions from Class V water at different depths

[0169] (1) Put Azolla imbricata 0258 in a low phosphate content state into a container with a depth of 50 cm and a surface area of 0.15 m 2 . The inoculation amount on the water surface is 60.0 - 80.0 g of fresh weight duckweed (coverage rate is about 100 - 130%). Under a white light LED lamp at room temperature of 25°C and a photosynthetic photon flux density of 110 μmol / m 2 / s, cultivate under full light for 2 days. Operations such as water body and duckweed sampling and determination are carried out as described in Control Example 1.

[0170] (2) At 0 h, 3 h, 6 h, 12 h, 24 h, 36 h, and 48 h of cultivation, water samples were taken at 0 cm, -5 cm, -10 cm, -15 cm, -20 cm, -25 cm, -30 cm, -35 cm, -40 cm, and -45 cm to measure the phosphate concentration in the water samples, and the removal rate of phosphate by duckweed was calculated. The results of the phosphate content in the water body and the average removal rate of phosphate by duckweed are as Figure 7 shown in Figures 7A and 7B. In the early stage of treatment, the deeper the water body, the lower the removal rate of phosphate by duckweed. The removal effect of the water surface closest to the duckweed (0 cm) is the fastest and best. The phosphate removal rate of the 0 cm water surface reaches 91.24% at 24 h. When standing for 2 days, the average removal rate of phosphate in the whole water body reaches more than 94%, and the average removal rate of phosphate on the 0 cm water surface reaches 97.10%. The removal rate under standing conditions is relatively high, but the phosphate removal flux is small, as Figure 7 shown in Figure 7E, and it is very time-consuming and laborious to change water and duckweed during actual operation.

[0171] Example 5: Removal of phosphate in Class V water at different depths under continuous flow conditions with duckweed in a low phosphate state

[0172] (1) The duckweed variety, phosphate content state, treatment container, photosynthetic photon flux density, temperature, and inoculation amount were all the same as those in Comparative Example 4, and it was cultured under full light for 7 days. The continuous flow conditions were an inlet water height of 2 cm, an outlet water height of 50 cm, and a flow rate of 34.7 mL / min. The operations of water body and duckweed sampling and measurement were all carried out as described in Comparative Example 1.

[0173] (2) At 0 h, 3 h, 6 h, 12 h, and 1 - 7 days of cultivation, water samples were taken at 0 cm, -5 cm, -10 cm, -15 cm, -20 cm, -25 cm, -30 cm, -35 cm, -40 cm, and -45 cm to measure the phosphate concentration in the water samples, and the removal rate of phosphate by duckweed was calculated. The results of the phosphate content in the water body and the average removal rate of phosphate by duckweed are as Figure 7 shown in Figures 7C and 7D. Compared with Comparative Example 4, the removal of phosphate at different depths in the water body by duckweed is more uniform. The phosphate concentration in the effluent reaches about that of Class II surface water. The average phosphate removal flux is as Figure 7 shown in Figure 7E, and the highest reaches 122.54 mg / m 2 / d, which is 24.81% higher than 98.18 mg / m 2 / d in Comparative Example 4. However, the continuous flow phosphate removal rate is not as high as that of standing, so the phosphate removal rate needs to be further optimized.

[0174] Comparative Example 5: Long - term removal of phosphate in Class V water under continuous flow conditions with duckweed in a low phosphate state under white light

[0175] (1) The duckweed variety, phosphate content status, treatment container, photosynthetic photon flux density, temperature, and inoculation amount were all the same as those in Comparative Example 4. The continuous flow conditions were an influent height of 2 cm, an effluent height of 50 cm, and a flow rate of 34.7 mL / min. White light full illumination culture was carried out for 16 days. Operations such as water body and duckweed sampling and determination were all carried out as described in Comparative Example 1.

[0176] (2) At 0 h, 3 h, 6 h, 12 h, and 1 - 16 days of cultivation, water samples were taken from the continuous effluent at 0 cm to measure the phosphate concentration in the water samples, and the removal rate of phosphate by duckweed was calculated. The results of the water body phosphate concentration, the removal rates of phosphate and ammonia nitrogen by duckweed, as well as the duckweed biomass yield, starch and protein contents, and starch and protein yields are as Figure 8 , Figure 9 , Figure 10 shown. The effluent phosphate and ammonia nitrogen concentrations tended to be stable after 3 days and 5 days of treatment respectively. After the effluent phosphate concentration stabilized, it basically remained slightly lower than the Class II water standard. The average phosphate removal rate was 78.33%, and the highest phosphate removal rate was 81.53%. The average phosphate removal flux was 103.12 mg / m 2 / d, and the highest phosphate removal flux was 111.42 mg / m 2 / d. After the effluent ammonia nitrogen concentration stabilized, the average ammonia nitrogen removal rate was 82.73%, and the highest ammonia nitrogen removal rate was 86.92%. The average ammonia nitrogen removal flux was 593.50 mg / m 2 / d, and the highest ammonia nitrogen removal flux was 635.28 mg / m 2 / d. The average biomass yield was 3.27 g / m 2 / d, and the highest biomass yield was 4.24 g / m 2 / d. The average starch content was 2.51%, and the highest starch content was 4.02%. The average starch yield was 0.08 g / m 2 / d, and the highest starch yield was 0.16 g / m 2 / d. The average protein content was 25.21%, and the highest protein content was 29.29%. The average protein yield was 0.82 g / m 2 / d, and the highest protein yield was 1.23 g / m 2 / d. It can be seen that the efficiency of duckweed in removing phosphate and ammonia nitrogen under white light is not high enough, and the biomass yield, starch and protein contents, and starch and protein yields are all relatively low.

[0177] (3) The phosphate, total nitrogen, and carbon fixation rates of duckweed are as Figure 11 shown. The average phosphate recovery rate was 19.35 mg / m 2 / d, and the highest phosphate recovery rate was 24.02 mg / m 2 / d. The average total nitrogen recovery rate was 131.07 mg / m2 / d, with the highest total nitrogen recovery rate being 196.53 mg / m 2 / d. The average carbon fixation rate is 1.28 g / m 2 / d, and the highest carbon fixation rate is 1.68 g / m 2 / d.

[0178] Example 6: Long - term removal of phosphate in Class V water under continuous - flow conditions with duckweed in a low - phosphate state under 90% red light

[0179] (1) The duckweed variety, phosphate content state, treatment container, photosynthetic photon flux density, temperature, and inoculation amount are all the same as in Comparative Example 4. The continuous - flow conditions are an inlet water height of 2 cm, an outlet water height of 50 cm, and a flow rate of 34.7 mL / min. It is cultured under 90% red - light full illumination for 16 days. Operations such as water body and duckweed sampling and measurement are all carried out as described in Comparative Example 1.

[0180] (2) At 0 h, 3 h, 6 h, 12 h, and days 1 - 16 of the culture, water samples are taken from the continuous outlet water at 0 cm to measure the phosphate concentration in the water samples, and the removal rate of phosphate by duckweed is calculated. The results of the phosphate content in the water body, the removal rates of phosphate and ammonia nitrogen by duckweed, as well as the duckweed biomass yield, starch and protein contents, and starch and protein yields are as Figure 8 、 Figure 9 、 Figure 10 shown. After 3 days of treatment, the concentrations of phosphate and ammonia nitrogen in the effluent tend to be stable. Calculated based on the current treatment capacity, the expected daily treatment volume of the duckweed red - light system reaches 333.12 L / m 2 / d, which can supply drinking water sources for 166 people (calculated at 2 L per person per day). The phosphate concentration in the effluent basically maintains around the Class I water standard, and the optimal effluent phosphate concentration reaches about 0.01 mg / L. After 3 days, the phosphate removal rate is stable above 90%. The average phosphate removal rate is 94.38%, and the highest phosphate removal rate reaches 98.20%. The average phosphate removal rate and the highest phosphate removal rate are increased by 20.49% and 20.44% respectively compared with Comparative Example 5. The average phosphate removal flux is 130.89 mg / m 2 / d, and the highest phosphate removal flux is 136.43 mg / m 2 / d. The average phosphate removal flux and the highest phosphate removal flux are increased by 26.93% and 22.45% respectively compared with Comparative Example 5. After 3 days, the ammonia - nitrogen removal rate is also stable above 90%. The average ammonia - nitrogen removal rate is 92.14%, and the highest ammonia - nitrogen removal rate reaches 94.46%. The average ammonia - nitrogen removal rate and the highest ammonia - nitrogen removal rate are increased by 11.54% and 8.66% respectively compared with Comparative Example 5. The average ammonia - nitrogen removal flux is 686.61 mg / m 2 / d, and the highest ammonia - nitrogen removal flux is 706.50 mg / m2 / d. The average ammonia nitrogen removal flux and the highest ammonia nitrogen removal flux are increased by 14.68% and 11.21% respectively compared with Comparative Example 5. The average biomass yield is 8.49 g / m 2 / d, and the highest biomass yield is 10.69 g / m 2 / d. The average biomass yield and the highest biomass yield are increased by 159.18% and 151.92% respectively compared with Comparative Example 5. The average starch content is 14.94%, and the highest starch content is 25.30%. The average starch content and the highest starch content are increased by 495.78% and 529.27% respectively compared with Comparative Example 5. The average starch yield is 1.28 g / m 2 / d, and the highest starch yield is 2.42 g / m 2 / d. The average starch yield and the highest starch yield are increased by 1410.64% and 1400.71% respectively compared with Comparative Example 5. The average protein content is 22.22%, and the highest protein content is 28.02%. The average protein content and the highest protein content are decreased by 13.43% and 4.52% respectively compared with Comparative Example 5. The average protein yield is 1.86 g / m 2 / d, and the highest protein yield is 2.34 g / m 2 / d. The average protein yield and the highest protein yield are increased by 127.13% and 90.54% respectively compared with Comparative Example 5. It shows that the application of the duckweed - red light system to the continuous removal of phosphate and denitrification in surface water with low phosphate pollution has a significant effect. Red light can simultaneously promote the removal ability of the duckweed system for phosphate and ammonia nitrogen, as well as the yields of biomass, starch, and protein.

[0181] (3) The phosphate, total nitrogen, and carbon fixation rates of duckweed are as Figure 11 shown. The average phosphate recovery rate is 31.00 mg / m 2 / d, and the highest phosphate recovery rate is 40.11 mg / m 2 / d. The average phosphate recovery rate and the highest phosphate recovery rate are increased by 60.22% and 66.99% respectively compared with Comparative Example 5. The average total nitrogen recovery rate is 297.70 mg / m 2 / d, and the highest total nitrogen recovery rate is 374.47 mg / m 2 / d. The average phosphate recovery rate and the highest phosphate recovery rate are increased by 127.13% and 90.54% respectively compared with Comparative Example 5. The average carbon fixation rate is 3.31 g / m 2 / d, and the highest carbon fixation rate is 4.30 g / m 2 / d. The average phosphate recovery rate and the highest phosphate recovery rate are increased by 159.25% and 155.83% respectively compared with Comparative Example 5. In addition, the power consumption of 90% red light is 0.741 kwh / m 2 / d, with an electricity consumption of 0.908 kwh / m less than that of white light 2 / d, reducing power consumption by 18.39%.

[0182] In summary, through the comparative analysis of the data in all the examples and comparative examples, it can be seen that in the examples, the water fern has an obvious effect on improving the phosphate removal rate of low-phosphate water bodies. Especially in Example 6, the water fern has significantly improved the removal of phosphate, ammonia nitrogen, biomass yield, starch and protein yields, and the harvesting effects of phosphate, total nitrogen, and carbon in Class V water, indicating that the method described in the present invention can simultaneously promote the removal of ammonia nitrogen and phosphate pollutants in surface water polluted by low phosphate and ammonia nitrogen, and also achieve the purpose of recycling and fixing phosphate, total nitrogen, and carbon. The system can also increase the biomass, starch, and protein yields of the water fern.

[0183] In addition, many reported technologies aim to achieve a high phosphate removal rate through small-volume treatment and extended treatment time. However, in practical applications, we prefer a large treatment volume, short treatment time, high removal rate, and fast and stable operation. Currently, many studies have shown that even if external phosphorus input is controlled, the internal phosphate load (such as sediment release) may still maintain a high nutrient state in the water body for a long time, leading to the persistence or deterioration of eutrophication problems. Therefore, the water fern red light system developed by us can not only continuously and efficiently remove phosphate in the water body, but also conveniently recycle the phosphate. This can not only prevent secondary pollution, but the recycled phosphate can also return to the terrestrial ecosystem for phosphorus cycling. Compared with other technologies, the continuous treatment method of water fern developed in the present invention has the capabilities of being fast, efficient, stable, and recyclable, and can provide an effective solution to the current dilemma of low phosphate pollution in surface water. Moreover, the operation of combining the water fern with the red light system in the present invention is simple, highly efficient in removing ammonia nitrogen and phosphate pollutants, and is also easy to promote on a large scale.

[0184] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only an example and does not constitute a limitation to this application. Although not explicitly stated here, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are proposed in this application, so such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this application.

[0185] Meanwhile, this application uses specific terms to describe the embodiments of this application. For example, "an embodiment", "one embodiment", and / or "some embodiments" mean a certain feature, structure, or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more at different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined.

Claims

1. A method for removing phosphorus pollution from water bodies using duckweed, characterized in that, It includes the following steps: planting duckweed in a low endogenous phosphate state on the surface of the polluted water body.

2. The method for removing phosphorus pollution in water body by using duckweed according to claim 1, characterized in that, In the duckweed in the low endogenous phosphate state, calculated by the fresh weight of the duckweed, the PO43--P in the duckweed is ≤ 0.5 mg / g; and / or The types of the duckweed in the low endogenous phosphate state include one or more of Spirodela polyrhiza 8410, Spirodela oligorrhiza 0202, Azolla filiculoides DWC132, Azolla filiculoides 8695, and Azolla filiculoides 0258; and / or The coverage rate of the duckweed on the surface of the polluted water body is 100% - 130%.

3. The method for removing phosphorus pollution from water body by using duckweed according to claim 1, characterized in that, The polluted water body is the polluted water body in a continuous flow treatment tank.

4. The method for removing phosphorus pollution in water body by using duckweed according to claim 3, characterized in that The continuous flow treatment tank is in a continuous flow mode of bottom inlet and top outlet, the flow rate of the continuous flow is V, and the depth of the continuous flow is H; and / or The removal rate of PO43--P in the effluent of the continuous flow is P1; and / or The removal rate of ammonia nitrogen in the effluent of the continuous flow is P2.

5. The method for removing phosphorus pollution in water body by using duckweed according to claim 4, characterized in that, V < 40 mL / min; and / or H < 60 cm; and / or The water output of the continuous flow is <384 L / m 2 / d; and / or 70% < P1 < 98.20%; and / or 80％＜P2＜94.46％。 6. The method for removing phosphorus pollution in water body by using duckweed according to claim 1, characterized in that Collect the duckweed after removing the phosphorus pollution in the water body. The biomass yield of the duckweed is M1, the starch content is M2, the starch yield is M3, the protein content is M4, the protein yield is M5, the phosphate recovery rate is M6, the total nitrogen recovery rate is M7, and the carbon fixation rate is M8; and / or The phosphorus concentration range of the polluted water body is C1, and the ammonia nitrogen concentration range is C2.

7. The method for removing phosphorus pollution in water body by using duckweed according to claim 6, characterized in that, M1 is 2.28 g / m 2 / d to 10.69 g / m 2 / d; and / or M2 is 1.23% - 25.30%; and / or M3 is 0.038 g / m 2 / d to 2.42 g / m 2 / d; and / or M4 is 14.74% - 28.02%; and / or M5 is 0.67 g / m 2 / d to 2.34 g / m 2 / d; and / or M6 is 13.99 mg / m 2 / d to 40.11 mg / m 2 / d; and / or M7 is 107.78 mg / m 2 / d to 374.47 mg / m 2 / d; and / or M8 is 0.92 g / m 2 / d to 4.30 g / m 2 / d; and / or C1 < 0.5 mg / L; and / or C2 < 2.5 mg / L.

8. The method for removing phosphorus pollution in water body by using duckweed according to claim 1, characterized in that After planting the duckweed in a low endogenous phosphate state on the surface of the polluted water body, it is placed under light conditions for cultivation. The light conditions are one or more of red light, blue light, green light, and white light.

9. The method for removing phosphorus pollution from water body by using duckweed according to claim 8, characterized in that, The red light is provided by a red LED lamp, with a peak wavelength of 660 nm, a full width at half maximum of 15 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s; and / or The blue light is provided by a blue LED lamp, with a peak wavelength of 450 nm, a full width at half maximum of 20 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s; and / or The green light is provided by a green LED lamp, with a peak wavelength of 520 nm, a full width at half maximum of 15 nm, and a photon flux density of 110 μmol / m 2 / s to 130 μmol / m 2 / s; and / or The white light is provided by a white LED lamp, and the photon flux density is 110 μmol / m 2 / s to 130 μmol / m 2 / s.

10. The method for removing phosphorus pollution from water body by using duckweed according to claim 8, characterized in that, The light conditions are red light and white light, and the proportion of the red light is 30% - 90%, and the balance is white light.

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