A method for repairing river and lake complex pollution by synergistically inhibiting algae and removing pollutants

Abstract

The present application belongs to the field of water environment treatment, and provides a river and lake complex pollution remediation method for synergistically inhibiting algae and removing pollutants, which comprises the following steps: (1) adding porous iron-based biochar and porous light filler into the sediment in the river or lake to be remediated, and mixing thoroughly to form a composite substrate; (2) planting aquatic plants with oxygen secretion ability on the composite substrate to remediate the river or lake; in the remediation process, the porous iron-based biochar catalyzes the oxygen secreted by the aquatic plant roots to form active oxygen species including hydroxyl radicals to oxidize and degrade organic pollutants in the river or lake and inhibit the growth of algae, and the porous iron-based biochar and the porous light filler adsorb and remove the pollutants in the river or lake. The present application can effectively enhance the removal capacity of the aquatic plants alone for the pollutants in the river or lake and the removal capacity of the aquatic plants alone for the algae in the river or lake, and improve the remediation effect for the complex pollution in the river or lake.

Description

Technical Field

[0001] The present invention belongs to the field of water environment management and relates to a method for repairing composite pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution. Background Art

[0002] In recent years, with the rapid development of agriculture, urbanization, and industrialization, human activities such as changes in land use and substandard discharge of industrial and agricultural wastewater have led to the long-term influx of pollutants such as nitrogen and phosphorus nutrients, heavy metals, and organic matter into rivers and lakes. These nutrients accumulate in overlying water and sediments, causing serious aquatic environmental and ecological problems. Nutrients such as nitrogen and phosphorus are key drivers of eutrophication, triggering the proliferation of algae such as cyanobacteria and green algae, as well as other organisms, leading to deterioration of water quality. Heavy metals commonly found in rivers and lakes, such as copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb), and mercury (Hg), accumulate in sediments through adsorption and may enter aquatic animals and humans through the food chain. Organic pollutants entering rivers, lakes, and reservoirs consume significant amounts of oxygen during decomposition, causing hypoxia in the water. This leads to the reductive decomposition of pollutants, producing numerous metabolic byproducts such as CH4 and H2S, which contribute to secondary environmental pollution. At the same time, these pollutants usually exist in the form of mixtures, most of which have ecological and environmental effects such as high toxicity, difficulty in degradation, easy enrichment and food chain amplification, forming a complex, dynamic and long-chain pollution system.

[0003] Using aquatic plants for water purification and ecological restoration is an economical and environmentally friendly method widely used in aquatic environments and water ecosystem management, such as rivers and lakes. Aquatic plants can directly reduce the concentrations of nitrogen and phosphorus nutrients, heavy metals, and organic pollutants in water bodies through direct absorption, thereby improving ecosystem stability. Furthermore, the oxygen and allelochemicals secreted by aquatic plant roots during growth, along with the attachment of specific root microbial communities, can drive the migration and degradation of pollutants. Current research on the use of aquatic plants for water purification and ecological restoration focuses primarily on the purification effects of aquatic plants through absorption and microbial metabolism. Furthermore, existing technologies focus primarily on the removal of specific pollutants by aquatic plants, with little research on the remediation of complex pollution using aquatic plants. However, aquatic plants have low mineralization rates for pollutants, are limited in their removal of specific pollutants, and have limited effectiveness in remediating complex pollution. Therefore, developing methods that effectively enhance plant-based pollutant removal and are applicable to the remediation of complex pollution in rivers, lakes, and reservoirs would have significant implications for the management and remediation of complex pollution in rivers and lakes. Summary of the Invention

[0004] In response to the problems of low pollutant removal rate, relatively single type of pollutants targeted, and poor remediation effect on complex pollution of rivers, lakes and reservoirs in existing methods of using aquatic plants for water purification and ecological restoration, the present invention provides a method for remediating complex pollution of rivers, lakes and reservoirs with synergistic algae inhibition and pollution removal, so as to effectively enhance the ability of individual aquatic plants to remove pollutants from rivers or lakes and reservoirs, and simultaneously enhance the ability to remove algae from rivers or lakes and reservoirs, thereby improving the remediation effect on complex pollution of rivers, lakes and reservoirs.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0006] A method for repairing complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution comprises the following steps:

[0007] (1) adding porous iron-based biochar and porous lightweight filler to the bottom mud of the river or lake to be remediated by composite pollution, and mixing them thoroughly to form a composite matrix;

[0008] (2) Aquatic plants with oxygen-secreting roots are planted on the composite matrix to carry out complex pollution remediation of rivers or lakes. During the complex pollution remediation process, the porous iron-based biochar catalyzes the oxygen secreted by the roots of the aquatic plants to form reactive oxygen species (ROS) including hydroxyl radicals. The reactive oxygen species oxidize and degrade organic pollutants in rivers or lakes while inhibiting the growth of algae. In addition, the porous iron-based biochar and porous lightweight fillers adsorb and remove pollutants in rivers or lakes.

[0009] In the above technical solution, in the composite matrix of step (1), the volume proportion of the bottom mud is preferably 50% to 60%, the volume proportion of the porous iron-based biochar is preferably 20% to 40%, and the volume proportion of the porous lightweight filler is preferably 10% to 30%.

[0010] In the above technical solution, porous iron-based biochar is primarily used to catalyze oxygen secreted by aquatic plant roots to form reactive oxygen species, including hydroxyl radicals. The porous iron-based biochar is obtained by thoroughly mixing an iron source and a carbon source and then calcining them in a single step. A feasible method for preparing porous iron-based biochar is as follows:

[0011] Bottom mud is taken from rivers or lakes, dried and crushed to obtain a carbon source, and the carbon source, iron source and chemical modifier are fully mixed to obtain a reaction precursor, and the reaction precursor is calcined at 600-1000°C for 2-4 hours in a nitrogen atmosphere to obtain porous iron-based biochar; the chemical modifier is hydrochloric acid, sulfuric acid, oxalic acid, alkali, oxalic acid, thiourea or sulfide.

[0012] In the above technical solution, when preparing porous iron-based biochar, the composition of the prepared porous iron-based biochar may vary depending on the type of active modifier, but the main active species of the porous iron-based biochar are usually zero-valent iron and Fe3C.

[0013] In the above technical solution, when preparing porous iron-based biochar, the carbon source content in the reaction precursor is preferably 80wt% to 90wt%, the iron source content is preferably 5wt% to 10wt%, and the chemical modifier content is preferably 5wt% to 10wt%.

[0014] In the above technical solution, when preparing porous iron-based biochar, the iron source is a water-soluble iron salt. Viable iron sources include hydrated or non-hydrated salts of ferric nitrate, ferric sulfate, ferrous sulfide, ferrous nitrate, ferrous sulfate, ferrous sulfide, etc.

[0015] In the above technical solution, when preparing porous iron-based biochar, taking sediment from a river or lake generally refers to taking sediment from a river or lake to be remediated by complex pollution.

[0016] In the above technical solution, the particle size of the porous iron-based biochar is in the micron level, and the particle size of the iron-based biochar can usually be 10nm to 100μm; the specific surface area of ​​the porous iron-based biochar is usually 10 to 300m 2 / g, and the pore volume is usually between 0.2 and 0.8 cm 3 Porous iron-based biochar can not only catalyze oxygen secreted by aquatic plant roots to form reactive oxygen species including hydroxyl radicals, but its porous structure can also adsorb and remove pollutants in rivers or lakes.

[0017] In the above technical solution, the porous lightweight filler is at least one of ceramsite, vermiculite, perlite, and volcanic rock. Furthermore, the porous lightweight filler is granular, preferably with a particle size of 3 to 10 mm. The porous lightweight filler not only provides support for aquatic plants but also absorbs nitrogen from retained water, providing a nitrogen source for the plants and promoting root oxygen secretion and oxygen transfer rates.

[0018] In the above technical solution, the aquatic plants include at least one of submerged plants with strong oxygen secretion ability in their root systems and emergent plants with strong oxygen secretion ability in their root systems. Furthermore, the aquatic plants are preferably at least one of Vallisneria, Myriophyllum, Ceratophyllum, Hydrilla, Potamogeton, Water Chestnut, Cattail, Juncus, Carex, Cyperus and Canna. In practical applications, the selection can be made based on the climate, water quality conditions and local aquatic plant types of the river or lake where the complex pollution remediation is to be carried out. Generally speaking, the submerged plants with strong oxygen secretion ability in their root systems and the emergent plants with strong oxygen secretion ability in their root systems can be staggered and reasonably matched in the same or multiple ways, combined with the local plant types, and local varieties can be given priority for planting.

[0019] In the above technical solution, the planting density of aquatic plants on the composite matrix is ​​determined by referring to existing technologies based on factors such as the type and variety characteristics of the aquatic plants (such as plant morphology, root distribution, growth rate) and the purification ability of the aquatic plants for pollutants.

[0020] In the above technical solution, when reactive oxygen species oxidize and degrade organic pollutants in rivers or lakes, they mainly degrade organic pollutants in the bottom mud of rivers or lakes, and can also degrade organic pollutants in the water body of rivers or lakes. In addition, reactive oxygen species can simultaneously inhibit the growth of benthic algae and phytoplankton in rivers or lakes. Since pollutants in the bottom mud of rivers or lakes mainly come from the water body, and pollutants in the bottom mud also affect the pollution of the water body, when the above technical solution is used to degrade organic pollutants in the bottom mud, the water pollution of rivers or lakes can be improved. In addition, the above technical solution can also effectively inhibit the outbreak of harmful algal blooms.

[0021] In the above technical solution, the pollutants in the rivers or lakes to be remediated for complex pollution primarily include nitrogen and phosphorus nutrients; heavy metals such as copper, chromium, cadmium, lead, and mercury; and organic substances such as persistent organic pollutants and emerging pollutants. When using the above technical solution of the present invention to remediate complex pollution in rivers, lakes, and reservoirs, the specific remediation time is determined based on the specific complex pollution situation of the river, lake, or reservoir, and the removal rate of the target pollutants and algae meets the actual application requirements. Typically, after 2 to 3 months of remediation, the complex pollution in the river or lake can be effectively controlled.

[0022] The restoration principle of the method for repairing river and lake complex pollution by synergistic algae inhibition and pollution removal of the present invention is as follows:

[0023] Porous iron-based biochar and porous lightweight fillers are added to the bottom mud of the river or lake to be remediated by complex pollution and fully mixed to form a composite matrix. Aquatic plants with oxygen-secreting roots are planted on the composite matrix. The porous iron-based biochar catalyzes a Fenton-like advanced oxidation process, the porous iron-based biochar and porous lightweight filler adsorb, the aquatic plant absorption and metabolic process, and the microbial metabolic decomposition process. The composite pollution is remediated from the two aspects of endogenous pollution control of river and lake sediments and water ecological restoration, as follows:

[0024] (1) Porous iron-based biochar activates oxygen secreted by the roots of aquatic plants to form reactive oxygen species including hydroxyl radicals. Hydroxyl radicals are a type of highly oxidizing reactive oxygen species that can not only efficiently degrade pollutants but also effectively inhibit the growth of algae, thereby effectively enhancing the ability of aquatic plants to degrade organic pollutants in rivers or lakes, while effectively inhibiting the growth of algae in rivers or lakes.

[0025] (2) Porous iron-based biochar and porous lightweight materials themselves have rich porous structures and large specific surface areas, which can remove nutrients, heavy metals, organic matter and other pollutants in rivers, lakes and reservoirs through one or more of the following adsorption mechanisms: hydrophilic interaction, electrostatic attraction / repulsion, polar attraction or non-polar attraction;

[0026] (3) Specific microorganisms are attached to the roots of aquatic plants. These microorganisms can quickly remove pollutants near the rhizosphere of aquatic plants through metabolism. At the same time, allelopathic substances such as polyphenols and sulfides secreted by the roots of aquatic plants can also inhibit the growth of algae. The porous iron-based biochar material will mediate the production of allelopathic substances secreted by the roots of deep-water plants to a certain extent, promoting the inhibition of algae.

[0027] (4) Aquatic plants themselves can also directly reduce nitrogen and phosphorus nutrients and organic pollutants in rivers or lakes through direct absorption.

[0028] Compared with the prior art, the technical solution provided by the present invention produces the following beneficial technical effects:

[0029] 1. The present invention provides a method for remediating complex pollution of rivers, lakes and reservoirs with synergistic algae inhibition and pollution removal. The method first adds porous iron-based biochar and porous lightweight filler to the bottom mud in the river or lake to be remediated for complex pollution, mixes them thoroughly to form a composite matrix, and then plants aquatic plants with oxygen-secreting roots on the composite matrix to remediate the pollution in the river or lake. In the pollution remediation process of the present invention, the porous iron-based biochar catalyzes the oxygen secreted by the roots of aquatic plants to form active oxygen species including hydroxyl radicals. The active oxygen species inhibit the growth of algae while oxidizing and degrading organic pollutants in rivers or lakes. The porous iron-based biochar and porous lightweight filler can adsorb and remove pollutants in rivers or lakes. At the same time, the aquatic plants can directly absorb and remove some pollutants in the river or lake for their growth. Through the combined effect of the above factors, the present invention effectively enhances the ability of individual aquatic plants to remove pollutants from rivers or lakes, and simultaneously enhances the ability to remove algae in rivers or lakes. The present invention can solve the problems of low pollutant removal rate, relatively single type of pollutants, and poor repair effect on complex pollution of rivers and lakes in methods using aquatic plants for water purification and ecological restoration, thereby improving the repair effect on complex pollution of rivers and lakes.

[0030] 2. The raw materials for preparing the porous iron-based biochar described in the present invention are cheap and easily available, and the preparation method is simple. By utilizing the cooperation of a composite matrix containing porous iron-based biochar, porous lightweight filler and bottom mud and aquatic plants with oxygen-secreting root systems, a porous iron-based biochar-catalyzed Fenton advanced oxidation process was successfully constructed. Reactive oxygen species including hydroxyl radicals were generated during the complex pollution remediation process. The present invention has confirmed through experiments that after 2 months of using the method of the present invention to repair the complex pollution of rivers or lakes, hydroxyl radicals with a concentration level of 90 to 110 μmol / kg were detected around the roots of aquatic plants. These hydroxyl radicals can significantly enhance the ability of individual aquatic plants to remove organic pollutants and algae in rivers or lakes.

[0031] 3. The method of the present invention can flexibly adjust the preparation process of iron-based biochar according to the actual water environment conditions of rivers and lakes, and then adjust the composition of porous iron-based biochar. At the same time, it can flexibly screen aquatic plants with oxygen-secreting root systems. It has the characteristics of flexibility and adaptability, and can be applied to the repair and treatment of complex pollution in various rivers or lakes. In addition, the method of the present invention is simple to operate, which is conducive to its promotion and application in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the restoration method for the synergistic algae inhibition and pollution removal of rivers, lakes and reservoirs according to the present invention.

[0033] Figure 2These are the test results of the removal rates of total nitrogen, total phosphorus, total organic carbon and green algae in river water in Example 1 and Comparative Example 1. The algae in the figure refer to green algae.

[0034] Figure 3 These are the test results for the removal rates of total nitrogen, total phosphorus, total organic carbon and green algae in river water in Comparative Example 2. The algae in the figure refer to green algae.

[0035] Figure 4 These are the test results for the removal rates of total nitrogen, total phosphorus, total organic carbon, and cyanobacteria in lakes in Example 2. The algae in the figure refer to cyanobacteria.

[0036] Figure 5 These are the test results for the removal rates of total nitrogen, total phosphorus, total organic carbon, and cyanobacteria in the reservoir in Example 3. The algae in the figure refer to cyanobacteria. DETAILED DESCRIPTION

[0037] The following examples further illustrate the method for remediating complex pollution in rivers, lakes, and reservoirs by synergistic algae inhibition and pollution removal described in the present invention. It should be noted that the following examples are intended only to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Based on the above disclosure, non-essential improvements and adjustments made by those skilled in the art to implement the present invention remain within the scope of protection of the invention.

[0038] Example 1

[0039] In this example, the method for remediating complex pollution in rivers and lakes by synergistic algae inhibition and pollution removal according to the present invention is described in detail. Specifically, the remediation process of complex pollution in rivers is simulated in a laboratory water tank. The size of the experimental water tank is determined according to the size of the river section to be remediated by complex pollution. The ratio of the size of the experimental water tank to the size of the river section to be remediated by complex pollution is controlled to be 1:100. The length of the river section to be remediated by complex pollution is about 600m. The steps are as follows:

[0040] (1) Take sediment from the river section to be remediated for complex pollution, remove rocks and large particles, and air-dry in the dark. Pulverize and pass through a 60-mesh sieve. Use the sieved dry sediment as the carbon source. Use ferric nitrate nonahydrate as the iron source and oxalic acid as the chemical modifier.

[0041] A carbon source, an iron source, and a chemical modifier are thoroughly ground and mixed to obtain a reaction precursor containing 85 wt% carbon source, 5 wt% iron source, and 10 wt% chemical modifier. The reaction precursor is calcined in a tube furnace at 800°C for 3 hours in a nitrogen atmosphere. The calcined product is thoroughly ground to obtain porous iron-based biochar with a particle size between 10 nm and 100 μm.

[0042] The specific surface area and pore structure of the porous iron-based biochar were characterized, and the surface element analysis showed that the specific surface area of ​​the porous iron-based biochar prepared in this step was 10-300 m 2 / g, and the pore volume is between 0.2 and 0.8 cm 3 / g, and the iron species mainly include zero-valent iron and Fe3C.

[0043] (2) The bottom mud was taken from the river section to be remediated by composite pollution and added to the experimental water tank. Then, porous iron-based biochar and porous lightweight filler were added and stirred thoroughly to form a composite matrix. In the composite matrix, the volume of the bottom mud accounted for 60%, the volume of the porous iron-based biochar accounted for 20%, and the volume of the porous lightweight filler accounted for 20%; the porous lightweight filler was spherical coal gangue ceramsite with a particle size of 8 mm.

[0044] Acorus calamus, an aquatic plant with oxygen-secreting roots, was planted on a composite substrate in an experimental water tank for remediation of the compound pollution. Rows were planted 10 cm apart, and plants were spaced 10 cm apart. Two to three calamus plants were planted in each hole. After planting, river water from the river section to be remediated was added to the experimental water tank. The river water contained 5 mg / L of total nitrogen, 1 mg / L of total phosphorus, and 5 mg / L of total organic carbon. The algae in the water were primarily green algae, with a chlorophyll a (Chla) concentration of 100 mg / L.

[0045] During the complex pollution remediation process, porous iron-based biochar catalyzes the oxygen secreted by the roots of Acorus calamus to form reactive oxygen species including hydroxyl radicals. The reactive oxygen species inhibit the growth of algae while oxidizing and degrading organic pollutants. The porous iron-based biochar and porous lightweight fillers adsorb and remove pollutants.

[0046] Two months after planting calamus to repair the complex pollution, water samples were taken from the experimental water tank to test the total nitrogen content, total phosphorus content, total organic carbon content and green algae concentration, and the total nitrogen removal rate, total phosphorus removal rate, total organic carbon removal rate and green algae removal rate were calculated. In this example, the total nitrogen removal rate of the river water was 80%, the total phosphorus removal rate was 85%, the green algae removal rate was 60%, and the total organic carbon removal rate was 70%.

[0047] Comparative Example 1

[0048] This comparative example employed a composite pollution remediation method essentially identical to that used in Example 1, except that the composite matrix was formed by mixing sediment and a porous lightweight filler, without the addition of porous iron-based biochar. The composite matrix consisted of 80% sediment by volume and 20% porous lightweight filler by volume.

[0049] Two months after planting calamus to repair the complex pollution, water samples were taken from the experimental water tank to test the total nitrogen content, total phosphorus content, total organic carbon content and green algae concentration, and the total nitrogen removal rate, total phosphorus removal rate, total organic carbon removal rate and green algae removal rate were calculated. In this comparative example, the total nitrogen removal rate of river water was 40%, the total phosphorus removal rate was 40%, the green algae removal rate was 10%, and the total organic carbon removal rate was 20%.

[0050] The test results of the removal rates of total nitrogen, total phosphorus, green algae and total organic carbon in river water in Example 1 and Comparative Example 1 are as follows: Figure 2 As shown. Figure 2 It can be seen that compared with Comparative Example 1, the total nitrogen removal rate, total phosphorus removal rate, total organic carbon removal rate and green algae removal rate of river water in Example 1 are significantly increased, with the increase rate reaching 50% to 85%. This is mainly due to the introduction of porous iron-based biochar, which cooperates with the oxygen secreted by the roots of aquatic plants to construct a Fenton-like advanced oxidation system, thereby effectively improving the ability of individual aquatic plants to remove pollutants and algae in rivers.

[0051] Comparative Example 2

[0052] In this comparative example, a composite pollution remediation method substantially the same as that in Example 1 was adopted, except that aquatic plants were not planted on the composite substrate.

[0053] After using the above method to repair the river complex pollution for 2 months, water samples were taken from the experimental tank to test the total nitrogen content, total phosphorus content, total organic carbon content and algae concentration, and the total nitrogen removal rate, total phosphorus removal rate, total organic carbon removal rate and green algae removal rate were calculated. The results are as follows: Figure 3 As shown, the total nitrogen removal rate of river water in this comparative example is 20%, the total phosphorus removal rate is 25%, the green algae removal rate is 8%, and the total organic carbon removal rate is 0%.

[0054] Combine Figures 2-3 As can be seen, compared with Comparative Example 2, Example 1 significantly increased the removal rates of total nitrogen, total phosphorus, green algae, and total organic carbon in river water, with increases exceeding 70%. This suggests that the composite matrix containing porous iron-based biochar itself has very limited ability to remove total nitrogen, total phosphorus, total organic carbon, and green algae from sediments. Only after aquatic plants with oxygen-secreting roots are planted on the composite matrix can they be used together with the porous iron-based biochar to construct a Fenton-like advanced oxidation system, utilizing the generated reactive oxygen species, including hydroxyl radicals, to enhance the removal of total nitrogen, total phosphorus, total organic carbon, and green algae.

[0055] Two months after the composite pollution of the river was repaired in Example 1 and Comparative Example 1, samples were taken from around the roots of the aquatic plants to detect the concentration of hydroxyl radicals. The results showed that the concentration of hydroxyl radicals detected around the roots of the aquatic plants in Example 1 was 70 μmol / kg, while almost no hydroxyl radicals were detected around the plants in Comparative Example 1. Two months after the composite pollution of the river was repaired in Comparative Example 2, the composite matrix was taken to detect the concentration of hydroxyl radicals. The results showed that no hydroxyl radicals were detected in the composite matrix of Example 2. This further illustrates that only after aquatic plants with oxygen-secreting roots are planted on the composite matrix containing porous iron-based biochar, the oxygen produced by the roots of the aquatic plants can be used together with the porous iron-based biochar to construct a Fenton-like advanced oxidation system to form reactive oxygen species including hydroxyl radicals to enhance the removal ability of pollutants and algae in the river.

[0056] Example 2

[0057] In this embodiment, the method for remediating complex pollution of rivers and lakes by synergistic algae inhibition and pollution removal of the present invention is described in detail. Specifically, the remediation process of complex pollution of lakes is simulated in a laboratory water tank. The size of the experimental water tank is determined according to the size of the lake area to be remediated by complex pollution. The ratio of the size of the experimental water tank to the size of the lake area to be remediated by complex pollution is controlled to be 1:100. The length of the lake area to be remediated by complex pollution is about 300m. The steps are as follows:

[0058] (1) Sediment was collected from the lake area to be remediated for complex pollution. Stones and large particles were removed. The sediment was air-dried in the dark and then crushed through an 80-mesh sieve. The sieved dry sediment was used as the carbon source. Ferric nitrate nonahydrate was used as the iron source, and oxalic acid was used as the chemical modifier.

[0059] A carbon source, an iron source, and a chemical modifier are thoroughly ground and mixed to obtain a reaction precursor containing 85 wt% carbon source, 5 wt% iron source, and 10 wt% chemical modifier. The reaction precursor is calcined in a tube furnace at 800°C for 4 hours in a nitrogen atmosphere. The calcined product is thoroughly ground to obtain porous iron-based biochar with a particle size between 10 nm and 100 μm.

[0060] (2) Bottom mud was taken from the lake area to be remediated for composite pollution and added to the experimental water tank. Then, porous iron-based biochar and porous lightweight filler were added and stirred thoroughly to form a composite matrix. In the composite matrix, the volume of the bottom mud accounted for 50%, the volume of the porous iron-based biochar accounted for 30%, and the volume of the porous lightweight filler accounted for 20%; the porous lightweight filler was volcanic rock with a particle size of 3.5 mm.

[0061] Vallisneria sinensis, an aquatic plant with oxygen-secreting roots, was planted on a composite substrate in an experimental water tank for remediation of the complex pollution. Rows were spaced 3 cm apart, and plants were spaced 3 cm apart. Three to four Vallisneria sinensis plants were planted in each hole. After planting, lake water from the lake area to be remediated was added to the experimental water tank. The lake water contained 7 mg / L of total nitrogen, 0.9 mg / L of total phosphorus, and 4 mg / L of total organic carbon. The algae in the water were primarily cyanobacteria, with a chlorophyll a (Chla) concentration of 80 mg / L.

[0062] During the complex pollution remediation process, porous iron-based biochar catalyzes the oxygen secreted by the roots of Vallisneria sinensis to form reactive oxygen species including hydroxyl radicals. The reactive oxygen species inhibit the growth of algae while oxidizing and degrading organic pollutants. The porous iron-based biochar and porous lightweight fillers adsorb and remove pollutants.

[0063] Two months after planting Vallisneria sinensis to repair the complex pollution of the lake, water samples were taken from the experimental tank to test the total nitrogen content, total phosphorus content, total organic carbon content and cyanobacteria concentration, and the total nitrogen removal rate, total phosphorus removal rate, total organic carbon removal rate and cyanobacteria removal rate were calculated. The results are as follows: Figure 4 As shown, the total nitrogen removal rate of lake water in this embodiment is 86%, the total phosphorus removal rate is 88%, the blue algae removal rate is 70%, and the total organic carbon removal rate is 75%.

[0064] Two months after the complex pollution of the lake was repaired in this example, samples around the roots of the aquatic plants were taken to detect the concentration of hydroxyl radicals. The results showed that the concentration of hydroxyl radicals around the roots of the aquatic plants was 90 μmol / kg.

[0065] Example 3

[0066] In this example, the method for remediating complex pollution in rivers and lakes by synergistic algae inhibition and pollution removal according to the present invention is described in detail. Specifically, the remediation process of complex pollution in a reservoir is simulated in a laboratory water tank. The size of the experimental water tank is determined according to the size of the reservoir area to be remediated by complex pollution. The ratio of the size of the experimental water tank to the size of the reservoir area to be remediated by complex pollution is controlled to be 1:100. The length of the reservoir area to be remediated by complex pollution is about 400m. The steps are as follows:

[0067] (1) Sediment was collected from the reservoir area to be remediated for composite pollution. Stones and large particles were removed, the sediment was air-dried in the dark, and then crushed through an 80-mesh sieve. The sieved dry sediment was used as the carbon source. Ferric nitrate nonahydrate was used as the iron source, and thiourea was used as the chemical modifier.

[0068] A carbon source, an iron source, and a chemical modifier are thoroughly ground and mixed to obtain a reaction precursor, wherein the carbon source content is 80wt%, the iron source content is 10wt%, and the chemical modifier content is 10wt%. The reaction precursor is placed in a tube furnace and calcined at 1000°C for 2 hours in a nitrogen atmosphere. The calcined product is thoroughly ground to obtain porous iron-based biochar with a particle size between 10nm and 100μm.

[0069] (2) Bottom mud was taken from the reservoir area to be remediated for composite pollution and added to the experimental water tank. Then, porous iron-based biochar and porous lightweight filler were added and stirred thoroughly to form a composite matrix. In the composite matrix, the volume of the bottom mud accounted for 50%, the volume of the porous iron-based biochar accounted for 30%, and the volume of the porous lightweight filler accounted for 20%; the porous lightweight filler was perlite particles with a particle size of 5 mm.

[0070] Snapdragons, aquatic plants with oxygen-secreting roots, were planted on a composite substrate in an experimental water tank for remediation of the complex pollution. Rows were spaced 4 cm apart, and plants were spaced 4 cm apart, with 3 to 4 plants planted per hole. After planting, reservoir water was added to the experimental water tank. The reservoir water, sourced from the reservoir area to be remediated, contained 6 mg / L of total nitrogen, 1.2 mg / L of total phosphorus, and 5 mg / L of total organic carbon. The algae in the reservoir water were primarily cyanobacteria, with a chlorophyll a (Chla) concentration of 78 mg / L.

[0071] During the complex pollution remediation process, porous iron-based biochar catalyzes the oxygen secreted by the snapdragon roots to form reactive oxygen species including hydroxyl radicals. The reactive oxygen species inhibit the growth of algae while oxidizing and degrading organic pollutants. The porous iron-based biochar and porous lightweight fillers adsorb and remove pollutants.

[0072] Two months after planting snapdragon to repair the complex pollution, water samples were taken from the experimental tank to test the total nitrogen content, total phosphorus content, total organic carbon content and cyanobacteria concentration, and the total nitrogen removal rate, total phosphorus removal rate, total organic carbon removal rate and cyanobacteria removal rate were calculated. The results are as follows: Figure 5 As shown, the total nitrogen removal rate of the reservoir water body in this embodiment is 90%, the total phosphorus removal rate is 85%, the blue algae removal rate is 90%, and the total organic carbon removal rate is 80%.

[0073] Two months after the composite pollution of the reservoir was repaired in this embodiment, samples around the roots of aquatic plants were taken to detect the concentration of hydroxyl radicals. The results showed that the concentration of hydroxyl radicals around the roots of the aquatic plants was 110 μmol / kg.

[0074] Those skilled in the art will appreciate that the embodiments described herein are intended to help those skilled in the art understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art may make various other specific variations and combinations based on the technical teachings disclosed herein without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A method for repairing complex pollution of rivers and lakes by synergistically inhibiting algae and removing pollution, characterized in that: The following steps are involved: (1) Porous iron-based biochar and porous lightweight filler are added to the bottom mud of the river or lake to be remediated by composite pollution, and are fully mixed to form a composite matrix; the main active species of the porous iron-based biochar are zero-valent iron and Fe3C, and the preparation method of the porous iron-based biochar is as follows: taking the bottom mud from the river or lake, drying and crushing it to obtain a carbon source, fully mixing the carbon source, the iron source and the chemical modifier to obtain a reaction precursor, and calcining the reaction precursor at 600-1000°C in a nitrogen atmosphere for 2-4 h to obtain porous iron-based biochar; the chemical modifier is hydrochloric acid, sulfuric acid, alkali, oxalic acid, thiourea or sulfide; (2) Aquatic plants with oxygen-secreting roots are planted on a composite matrix to remediate pollution in rivers or lakes. During the pollution remediation process, the porous iron-based biochar catalyzes the oxygen secreted by the roots of the aquatic plants to form reactive oxygen species including hydroxyl radicals. The reactive oxygen species oxidize and degrade organic pollutants in rivers or lakes while inhibiting the growth of algae. In addition, the porous iron-based biochar and porous lightweight fillers adsorb and remove pollutants in rivers or lakes.

2. The method for repairing river and lake complex pollution by synergistic algae inhibition and pollution removal according to claim 1 is characterized in that: In the composite matrix of step (1), the volume proportion of the bottom mud is 50% to 60%, the volume proportion of the porous iron-based biochar is 20% to 40%, and the volume proportion of the porous lightweight filler is 10% to 30%.

3. The method for repairing complex pollution of rivers and lakes by synergistic algae inhibition and pollution removal according to claim 1 is characterized in that: In the reaction precursor, the content of the carbon source is 80 wt% to 90 wt%, the content of the iron source is 5 wt% to 10 wt%, and the content of the chemical modifier is 5 wt% to 10 wt%.

4. The method for repairing complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution according to claim 1 is characterized in that: The iron source is a water-soluble iron salt.

5. The method for remediating complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution according to any one of claims 1 to 4, characterized in that: The particle size of porous iron-based biochar is in the micron range.

6. The method for remediating complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution according to any one of claims 1 to 4, characterized in that: The porous lightweight filler is at least one of ceramsite, vermiculite, perlite and volcanic rock.

7. The method for repairing complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution according to claim 6 is characterized in that: The porous lightweight filler is in granular form with a particle size of 3 to 10 mm.

8. The method for remediating complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution according to any one of claims 1 to 4, characterized in that: The aquatic plants include at least one of submerged plants whose roots have the ability to secrete oxygen and emergent plants whose roots have the ability to secrete oxygen.

9. The method for repairing complex pollution of rivers, lakes and reservoirs by synergistically inhibiting algae and removing pollution according to claim 8 is characterized in that: The aquatic plants include at least one of Vallisneria, Foxtail Algae, Ceratophyllum, Hydrilla, Potamogeton truncatum, Water Chestnut, Cattail, Juncus, Carex, Cyperus and Canna.

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