A method and application of promoting the growth of aquatic biological crusts by knotweed to repair heavy metal pollution

Abstract

The present invention provides a method and application of using sedge to promote the growth of aquatic biological crusts to jointly repair heavy metal pollution. The algae in the aquatic biological crust can continuously and automatically produce alkali, which can effectively improve the pH of the tailings drainage while achieving the fixation of heavy metals, and is conducive to the survival and settlement of other plants or animals. For example, after the repair, there are small animals such as fish in the tailings drainage, and the ecological restoration effect is good. The selected sedge is a perennial fern, which has much higher tolerance to heavy metals than other plants and is very easy to reproduce. Its fallen leaves can be used as nutrients to provide nutrition for subsequent algae and other wetland plants. Aquatic biological crust is a kind of algae-mineral complex. The cost of deployment and maintenance is low, the fixation effect on heavy metals is good and long-lasting, and the disturbance to the surrounding environment is small.

Description

Technical Field

[0001] The present invention relates to the field of environmental restoration, and in particular to a method and application of a joint restoration method for heavy metal pollution using aquatic biocrusts promoted by knotweed. Background Art

[0002] Metal mining and post-mining tailings dumping, among other related processes, cause serious geological disasters, soil pollution, and ecological and environmental problems. Tailings ponds are composed of accumulated tailings sand. This type of tailings has a loose and porous matrix with extremely poor water and fertilizer retention, making it completely different from conventional soil. Tailings are rich in various toxic metals and high in sulfur, which can severely damage the ecological environment. The acidic mine water caused by the oxidation of sulfides can further leach heavy metals, making the mine water often rich in heavy metals such as Cd and As. This is one of the main sources of heavy metal pollution in mining areas and surrounding water and soil worldwide. In the hot and rainy southern region, the drainage of tailings wetlands is more likely to lead to the formation of natural wetlands, causing long-term damage to the surrounding environment and soil.

[0003] Revegetation and restoration of biocapacity are fundamental measures for remediating mining wastelands and controlling heavy metal pollution. Wetland sediments are generally considered sinks for heavy metals. Reduced heavy metal concentrations are typically higher in anoxic zones, resulting in lower bioavailability of heavy metals compared to terrestrial systems with oxidized soils. Plant roots in wetlands have limited reach, limiting the rhizosphere's ability to absorb pollutants. Heavy metals typically bind to sulfides in the anoxic sediments at the riverbed after entering the riverbed. However, oxygen can migrate downward through plant stomata to the roots, further oxidizing the sediment near their roots. This facilitates the transport of heavy metal pollutants and increases their bioavailability, making it difficult for wetland plants to survive. For tailings wetland ecosystems, excessively high nutrient levels in sediments can stress plant seed germination and even be toxic to seedling growth, thus compromising the overall restoration process. To accelerate this restoration process, artificially assisted plant restoration is often used. The primary challenges of artificially assisted plant restoration are successful root establishment and biomass expansion. Biological crusts are a type of biological cementation layer formed by algae and other microorganisms through processes such as secreting extracellular polymers to agglomerate mineral particles. Aquatic biological crusts (BACs) are a new type of biological crust found in polymetallic tailings drainage in South China. They are mainly composed of inorganic minerals (clay minerals and iron-manganese oxides, etc.) and organic matter (including rich microbial communities and their extracellular secreted polymers). Due to their special structural composition, they have extremely strong heavy metal enrichment capabilities and can simultaneously and effectively fix heavy metals in tailings drainage. The cyanobacteria and green algae in biological crusts can colonize the mineral matrix, and the accumulated organic matter can also bridge with silicates and iron-containing compounds to form organic-mineral complexes, which can serve as a medium carrier to replace sediments to a certain extent to help wetland plants colonize. At the same time, aquatic biological crusts can reduce the concentration of heavy (metal) metals in tailings drainage and improve its water quality to a certain extent. They can serve as a nature-based solution for in situ remediation of tailings drainage.

[0004] To address the serious heavy metal contamination in tailings drainage, current treatment technologies primarily include physical, chemical, and biological methods. Because other methods for treating tailings drainage are costly to construct and maintain, and their in-situ application significantly disrupts the local ecological environment, biological treatment is more suitable for tailings drainage remediation.

[0005] Compared with physical and chemical methods, bioremediation has less disturbance to the local environment and is conducive to local ecological restoration. For heavy metal pollution in tailings drainage, an artificial wetland model using wetland plants would be a better treatment method. The main patents include: an artificial wetland treatment system for eutrophic water bodies using steelmaking waste slag as a matrix, which adopts a horizontal subsurface artificial wetland model and consists of an artificial wetland pool, a matrix layer, a wetland plant system and a water distribution system. It is suitable for the purification and restoration of high turbidity, high N and P eutrophic water bodies in villages and towns (CN101514053B). A method for treating acidic mine wastewater, by adding Thiobacillus ferrooxidans and humic acid to the acidic mine wastewater and aerating it at the same time, can cause biomineralization in the acidic mine wastewater, forming secondary iron minerals, and co-precipitating heavy metals such as dissolved iron, Cd and Pb in the acidic mine wastewater, achieving the purpose of efficiently and quickly removing dissolved iron and heavy metals in the acidic mine wastewater (CN112694176B). Acidic mine wastewater is biomineralized by acidophilic iron-oxidizing bacteria, then circulated and bioreduced by acidophilic iron-reducing bacteria, and then enters an alkaline regulating tank for pH adjustment. The effluent is then circulated to a biomineralization treatment unit for circulatory treatment (CN111620444B). A method of reducing the heavy metal content of acidic mine wastewater and adjusting its pH in a gravel pool is used. The acidic mine wastewater is then slow-flowed, and plants are used to further absorb the heavy metals and some of the sulfate ions. The microbial pool is then treated with microorganisms to increase the pH value. The water quality is improved through absorption and adsorption by trees and carbonized straw particles. Finally, a medical stone filter valve is used to sterilize and improve the treated water quality, thereby establishing an effective and pollution-free ecological treatment system for acidic mine wastewater (CN106927639B). However, the application of plants or microorganisms for remediation requires the cooperation of other facilities, which may still cause certain ecological damage or the effect on heavy metals in tailings drainage may not be significant and rapid enough. The application of wetland plant-aquatic biological crust system can effectively fix heavy metals without disturbing the local environment.

[0006] The microorganisms in the crust can utilize the fallen leaves of plants, and the root secretions of plants may also promote the growth of crusts to a certain extent. Therefore, the plant-crust repair system is theoretically possible. At present, the application of the plant-crust system is mainly focused on the remediation of contaminated soil and there are few related cases. Xu Zaixian et al. used algae culture medium, soil fixative and super absorbent material to cultivate a composition for ecological restoration of barren land to generate soil crusts to repair ecological wastelands (composition for ecological restoration and ecological restoration method using the same, authorization announcement number: CN105521989B). The application of the wetland plant-aquatic organism crust repair system can achieve the effect of fixing a large amount of metals in tailings drainage. Therefore, we proposed a nature-based solution to construct an artificial wetland system of wetland plant-aquatic organism crusts to fix heavy metals in tailings drainage. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for promoting the growth of aquatic biological crusts by using knotweed to jointly repair heavy metal pollution.

[0008] Another object of the present invention is to provide application of the above method in treating tailings wastewater.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for promoting the growth of aquatic biocrusts by using knotweed to repair heavy metal pollution, comprising the following steps:

[0011] (1) adding wild aquatic organism crusts into a culture medium to multiply and obtain an aquatic organism crust culture medium, and pretreating artemisia argyi seeds to obtain artemisia argyi seedlings;

[0012] (2) Planting knotweed seeds in the upper reaches of polluted rivers to form a plant grid;

[0013] (3) Planting the knotweed seedlings obtained by the pretreatment in step (1) in the middle reaches of the polluted river, and adding aquatic biological crust culture medium to promote the growth of aquatic biological crust.

[0014] The wild aquatic biological crust (BAC) described in step (1) is a special complex formed by the combination of inorganic minerals and organic matter, and has a very strong ability to accumulate heavy metals.

[0015] The culture medium in step (1) is BG-11 culture medium.

[0016] The specific steps of the expansion described in step (1) are:

[0017] Take 10-20 g of crust of wild aquatic organisms, add it into a flask with 100 ml of distilled water, shake it, let it stand and separate the layers, take 10 ml of the supernatant, add it into 1 L of BG-11 culture medium, and culture it for 2-3 weeks. The lighting conditions are fluorescent lamp, the light intensity is 8000 lx, and the lighting time is 12 hours of light and 12 hours of darkness.

[0018] The pretreatment of the sedge seeds in step (1) is to soak the sedge seeds in a 1-2% white sugar aqueous solution for 24-48 hours, and obtain sedge seedlings after the sedge seeds germinate.

[0019] The polluted river described in steps (2) and (3) is a heavy metal polluted river; preferably, it is a polluted river downstream of a lead-zinc tailings pond.

[0020] The planting density in step (2) is 7 to 15 plants / m 2 ; preferably 10 plants / m 2 .

[0021] The scutellaria seeds described in step (2) are scutellaria seeds soaked in 5-10% H2O2 for 1-2 hours.

[0022] The planting density in step (3) is 2 to 4 plants / m 2 ; preferably 3 plants / m 2 .

[0023] The amount of the aquatic biological crust culture medium added in step (3) is 0.1 to 0.5 g / strain based on the dry weight of the microorganisms.

[0024] The above-mentioned method of promoting the growth of aquatic biological crusts by knotweed and combining it with the repair of heavy metal pollution is applied in the treatment of tailings wastewater.

[0025] The present invention has the following advantages and effects compared to the prior art:

[0026] (1) The combined restoration model of aquatic biocrust and sedge grass was selected, which has a strong heavy metal removal effect and can achieve batch fixation of heavy metals, thereby reducing the harm of tailings drainage to the surrounding ecological environment. The algae in the aquatic biocrust can also continuously and automatically produce alkali, which can effectively improve the pH of the tailings drainage while achieving heavy metal fixation, and is conducive to the survival and settlement of other plants or animals. For example, small animals such as fish are found in the tailings drainage after restoration, and the ecological restoration effect is good.

[0027] (2) The selected perennial fern, A. truncatula, is much more tolerant to heavy metals than other plants and is highly reproducible. Its fallen leaves can serve as nutrients for subsequent algae and other wetland plants. Aquatic biocrusts are algae-mineral complexes with low deployment and maintenance costs. They have a strong and long-lasting effect on heavy metal fixation and minimal disturbance to the surrounding environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the knotweed that promotes the function of aquatic biological crust formation (Figures a, b, and c are photos of the different stages of knotweed promoting crust formation, and Figure d shows that knotweed replaces other wetland plants (such as reeds) to become the only dominant species in the crust system).

[0029] Figure 2 This is a photo of the growth of aquatic biological crusts in the knotweed wetland one year after planting.

[0030] Figure 3 This is a photo of the growth of aquatic biological crusts in the reed wetland one year after planting.

[0031] Figure 4 This is a graph showing the results of the determination of heavy metal element content in the upstream and downstream areas of aquatic biological crusts.

[0032] Figure 5 This is a conceptual diagram of the three-dimensional restoration model formed by aquatic biological crusts and knotweed. DETAILED DESCRIPTION

[0033] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0034] If specific experimental conditions are not specified in the following embodiments, conventional experimental conditions or those recommended by the reagent company will generally be used. Materials and reagents used were commercially available unless otherwise specified.

[0035] Example 1

[0036] 1. Artificial propagation of wild aquatic crusts

[0037] Aquatic crusts were collected from an abandoned lead-zinc tailings pond in Meizhou, Guangdong. 10 g of the collected aquatic crusts were added to a flask with 100 ml of distilled water and shaken for 1 hour. After standing and stratification, 10 ml of the supernatant was taken and added to 1 LBG-11 culture medium. The culture was carried out for 2 weeks under fluorescent lighting (8000 lx 12 h light and 12 h dark). After drying, the aquatic crusts were obtained after propagation.

[0038] In order to determine the microbial community composition of aquatic crust, the microbial population in the crust was sampled and identified. The main communities were 25% RD017, 10% TG-45, 10% Amphiplicatus, 20% Leptolyngbyaceae, 10% A4b, and 25% Cytophagales. Existing literature has disclosed that aquatic crust can effectively treat heavy metal pollution in water bodies. For details, please refer to the literature Wang G, Yuan Y, Morel JL, et al. Biological aqua crust mitigates metal (loid) pollution and the underlying immobilization mechanisms [J]. Water Research, 2021, 190 (1): 116736.

[0039] The culture medium used was the classic BG11 algae culture medium (pH 7.4). The detailed formula is shown in the following table:

[0040] Table 1 Composition of BG11 medium

[0041] serial number Culture medium components <![CDATA[Concentration g·L -1 > 1 <![CDATA[NaNO3]]> 1.5 2 <![CDATA[K2HPO4·3H2O]]> 0.04 3 <![CDATA[MgSO4·7H2O]]> 0.075 4 <![CDATA[CaCl2·2H2O]]> 0.036 5 citric acid 0.006 6 Ammonium ferric citrate 0.006 7 EDTA 0.001 8 <![CDATA[Na2CO3]]> 0.02 9 Trace metal mix A5+Co* <![CDATA[1mL·L -1 ]]> 9.1 <![CDATA[H3BO3]]> <![CDATA[2.86g·L -1 ]]> 9.2 <![CDATA[MnCl2·4H2O]]> <![CDATA[1.81g·L -1 ]]> 9.3 <![CDATA[ZnSO4·7H2O]]> <![CDATA[0.222g·L -1 ]]> 9.4 <![CDATA[Na2MoO4·2H2O]]> <![CDATA[0.390g·L -1 ]]> 9.5 <![CDATA[CuSO4·5H2O]]> <![CDATA[0.079g·L -1 ]]> 9.6 <![CDATA[Co(NO3)2·6H2O]]> <![CDATA[0.0494g·L -1 ]]>

[0042] *: 9.1 to 9.6 are the specific components of trace metal mix A5+Co.

[0043] 2. Pretreatment of knotweed seeds

[0044] Ten days before sowing, the shade-dried knotweed seeds were soaked in a 1% white sugar aqueous solution in the laboratory for 24 hours. After the knotweed seeds germinated, the knotweed seedlings were obtained, and the seedlings were transplanted into the contaminated tailings drainage mud.

[0045] For comparison, reed seeds were treated in the same way and reed seedlings were obtained after germination and transplanted.

[0046] Example 2 Aquatic organism crust growth promotion experiment

[0047] In the middle reaches of the wetland, a river channel with a depth of about 0.5 m was selected to set up an artificial wetland area with a length of 200 m and a width of 10 m. The knotweed seedlings and reed seedlings obtained in step 2 of Example 1 were cultivated by cuttings, respectively, with a planting density of 3 plants / m 2 After the planting was completed, the aquatic biological crust obtained in step 1 of Example 1 was spread on the roots of the plants. The dosage was 0.1 g / plant based on the dry weight of microorganisms. Three areas were set for each plant as repeated experiments.

[0048] 10 days after planting, check the growth of aquatic biological crusts. Figure 1 As shown, the roots of the knotweed successfully promoted the growth of a large number of aquatic biocrusts ( Figure 1 a~ Figure 1 c) It proves that the knotweed can effectively promote the formation of crusts on aquatic organisms; while the roots of reeds almost do not produce crusts ( Figure 1 d) It proves that reeds cannot promote the growth of aquatic biological crusts; after one year of planting, the crust growth was checked again. The results are as follows Figures 2-3 As shown, the wetlands planted with phragmites still maintained a large amount of aquatic crusts, while the reed wetlands still did not produce any. This shows that compared to wetland plants such as reeds, phragmites has greater tolerance and survival ability and a stronger root system, making it more compatible with aquatic crusts. Subsequent experiments will use phragmites to promote the growth of aquatic crusts.

[0049] Example 3: Joint repair of heavy metal pollution by promoting the growth of aquatic biocrusts with scutellaria baicalensis

[0050] In this example, the restoration model was applied in a wetland downstream of a lead-zinc tailings pond in South China by combining a vegetative grid with a vegetative crust promoted by aquatic organisms. The tailings drainage containing a large amount of heavy metals produced by the tailings accumulation was repaired. The specific steps are as follows:

[0051] (1) Planting of knotweed plant grid upstream

[0052] Planting of sedge grass in the upstream river channel of the wetland to form a plant grid; soaking sedge grass seeds in 10% H2O2 for 1 hour, drying them in the shade, and evenly sowing them on the surface of the bottom mud (5 cm). The planting density of sedge grass in the plant grid area is 10 plants / m 2 The area's knotweed should be promptly harvested and cleared to ensure optimal growth and maximize heavy metal retention in the water. Densely planted knotweed forms a vegetative grid, where its roots can bind numerous mineral particles in the tailings drainage, lowering the pH and heavy metal content, initially reducing contamination and creating conditions for the formation of a crust. Care should be taken to minimize rapid water flow and ensure the riverbed substrate is not too hard to prevent plant growth. Ideally, a wetland-like state should be established before seeding.

[0053] (2) Using knotweed to promote the growth of aquatic biocrusts to create artificial wetlands

[0054] An aquatic biological crust treatment group was set up in the middle reaches of the wetland river, and knotweed was planted to promote the formation of aquatic biological crust; a river with a depth of about 0.5m was selected, and an artificial wetland area with a length of 200m and a width of 10m was set up. The knotweed seedlings obtained in Example 1 were cultivated by cuttings, and the knotweed planting density was 3 plants / m 2After the planting is completed, the expanded aquatic biological crust culture medium obtained in Example 1 is spread around the roots of the knotweed, and the dosage is 0.1g / plant in terms of microorganisms. The knotweed in this area does not need to be cleaned for a long time, and its root system is well developed. The root secretions and litter can be used by the microorganisms in the crust to promote the formation of the crust; the setting method is shown in the schematic diagram Figure 5 shown.

[0055] (3) Testing and judgment of the combined repair effect

[0056] When the growth of the upstream knotweed was stable and the aquatic biological crust in the middle reaches of the artificial wetland was successfully promoted, the river water in the front, middle and rear sections of the artificial wetland and the upstream of the artificial wetland was sampled and tested to verify the treatment effect. The pH of the river water in this section was measured on site using a portable water quality parameter analyzer. After acidification, it was brought back to the laboratory and filtered through a 0.45um filter membrane. The heavy metal element content was determined using ICP-OES. The results are as follows Figure 4 As shown, the pH value rose from acidity to near neutral after passing through the plant grid area. After passing through the crust-sedge area, the heavy metal content was reduced by more than 70%. During the experimental period (2019.6-2022.6), no exogenous addition and management were required, and the repair effect was stable and good. The results proved that aquatic biological crusts have a good repair effect on heavy (type) metals in water.

[0057] As a typical metal-tolerant plant, scutellaria not only serves as a key carrier of aquatic biocrusts but also promotes the growth of microorganisms within these crusts through root secretions. Furthermore, the biocrusts themselves promote the proliferation of scutellaria. The two complement each other, allowing them to coexist effectively in oligotrophic, high-heavy-metal habitats like tailings drainage, thereby forming an efficient and low-cost three-dimensional wetland restoration model.

[0058] As a type of organic-mineral complex, the process of formation of aquatic biological crust is also a process of utilizing the high concentration of heavy metal ions and mineral particles in tailings drainage. At the same time, the rich photosynthetic autotrophic organisms and nitrogen-fixing microorganisms in it can promote the accumulation of nutrients such as carbon and nitrogen in the aquatic biological crust and knotweed system, so that the sustainable remediation of heavy metals in tailings drainage can be achieved.

[0059] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for promoting the growth of aquatic biocrusts by using knotweed to repair heavy metal pollution, characterized in that The following steps are involved: (1) adding wild aquatic organism crusts into a culture medium to multiply and obtain an aquatic organism crust culture medium, and pretreating artemisia argyi seeds to obtain artemisia argyi seedlings; (2) Planting knotweed seeds in the upper reaches of polluted rivers to form a plant grid; (3) Planting the knotweed seedlings obtained by the pretreatment in step (1) in the middle reaches of the polluted river, and adding aquatic biological crust culture medium to promote the growth of aquatic biological crust.

2. The method according to claim 1, wherein: The wild aquatic biological crust (BAC) described in step (1) is a special complex formed by the combination of inorganic minerals and organic matter, and has a very strong ability to accumulate heavy metals.

3. The method according to claim 1, wherein: The culture medium in step (1) is BG-11 culture medium.

4. The method according to claim 3, characterized in that The specific steps of the expansion described in step (1) are: Take 10-20 g of crust of wild aquatic organisms, add it into a flask with 100 ml of distilled water, shake it, let it stand and separate the layers, take 10 ml of the supernatant, add it into 1 L of BG-11 culture medium, and culture it for 2-3 weeks. The lighting conditions are fluorescent lamp, the light intensity is 8000 lx, and the lighting time is 12 hours of light and 12 hours of darkness.

5. The method according to claim 1, wherein: The pretreatment of the sedge seeds in step (1) is to soak the sedge seeds in a 1-2% white sugar aqueous solution for 24-48 hours, and obtain sedge seedlings after the sedge seeds germinate; The scutellaria seeds described in step (2) are scutellaria seeds soaked in 5-10% H2O2 for 1-2 hours.

6. The method according to claim 1, wherein: The polluted river described in steps (2) and (3) is a heavy metal polluted river.

7. The method according to claim 1, wherein: The planting density in step (2) is 7 to 15 plants / m 2 .

8. The method according to claim 1, wherein: The planting density in step (3) is 2 to 4 plants / m 2 .

9. The method according to claim 1, wherein: The amount of the aquatic biological crust culture medium added in step (3) is 0.1 to 0.5 g / strain based on the dry weight of the microorganisms.

10. Use of the method of promoting the growth of aquatic biological crusts by Herba Lycopodii as described in any one of claims 1 to 9 in the treatment of tailings wastewater.

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