Pteris vittata repair efficiency evaluation method and application thereof

Abstract

The invention discloses a ciliate desert-grass repair efficiency evaluation method and application thereof, and aims to solve the problem that arsenic-rich biomass recycling lacks scientific quality standards. According to the method, the total arsenic concentration and the total flavone concentration of the overground part of the ciliate desert-grass are innovatively combined, a comprehensive evaluation index is constructed, and the harvested biomass is scientifically graded according to the comprehensive evaluation index. Based on the evaluation result, qualified biomass is directionally prepared into an efficient iron-modified biochar adsorbent through the steps of pyrolysis, iron modification and the like, the efficient iron-modified biochar adsorbent is used for treating arsenic-containing wastewater, safe solidification and high-value utilization of pollutants and recycling of water resources are achieved, and remarkable environmental benefits and economic values are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental biotechnology and resource recycling, and specifically relates to a method for evaluating the remediation efficiency of Pteris vittata and application thereof. BACKGROUND

[0002] Natural geological activities (such as volcanic eruption, rock weathering) are the natural source of arsenic in the environment, but human activities, especially mining, non-ferrous metal smelting (copper, lead, zinc, gold), the burning of fossil fuels (especially coal), the excessive use of arsenic-containing pesticides and herbicides, wood preservation treatment, and the microelectronics industry, have become the main driving force for the rapid increase in the concentration of arsenic in the local environment. In the process of mining and processing of sulfur-containing minerals, discarded ore and tailings piles react with oxygen and water in the atmosphere to cause sulfide oxidation, which not only releases a large amount of soluble arsenic, but also produces strong acid, high sulfate-containing wastewater commonly known as "acid mine drainage". The pH of such wastewater is often as low as 2-4, with high concentrations of arsenic and iron, manganese, copper, cadmium, lead and other heavy metal ions dissolved therein. Once such pollution enters the surrounding surface water system and farmland soil through surface runoff or underground infiltration, it will cause persistent and difficult-to-reverse ecological disasters, and through the "soil-plant-animal / human" food chain, it will eventually pose a serious and direct threat to human health.

[0003] Arsenic-contaminated soil is very difficult to remediate. In this context, phytoremediation technology exhibits unique advantages due to its green, in-situ, low cost, small environmental disturbance, and ecological aesthetic value. This technology uses the synergistic effect of specific plants and their rhizosphere microbial systems to extract, root-fix, volatilize or transform pollutants in the soil. Among them, phytextraction, which uses hyperaccumulator plants to efficiently absorb pollutants from the soil and transport and accumulate them in the harvestable part of the plant, is considered the most effective way to completely remove heavy metal pollutants from the soil. Pteris vittata is the first arsenic hyperaccumulator discovered by the scientific community, which exhibits amazing tolerance and enrichment capacity for arsenic. Numerous studies have confirmed that Pteris vittata can accumulate up to 22.6 g / kg (dry weight) of arsenic in its aerial part of pinnae, and the arsenic concentration in its aerial tissues can reach thousands of times that of the growth medium (soil).

[0004] Although phytoremediation has a broad prospect, its wide application and industrialization process has been subject to a key bottleneck: the subsequent safe disposal and management of plant biomass enriched with high concentrations of arsenic. Improper disposal will make the remediation work in vain. Traditional disposal methods have serious defects: safe landfill not only occupies a large amount of valuable land resources, but also in the complex physical, chemical and microbial environment of landfill, biomass degradation may lead to the transformation and activation of arsenic, there is a long-term risk of re-release and pollution of groundwater due to leaching; direct incineration, although it can greatly reduce the volume of biomass, but in the process, arsenic and its compounds (especially arsenic trioxide ) have a low boiling point, are extremely easy to volatilize into the atmosphere, causing air pollution, and the unvolatile arsenic is highly enriched in fly ash and bottom ash, forming a more toxic and more difficult to dispose of hazardous waste; the composting process is long, and the transformation and migration rules of arsenic in the composting process and the stability of the final product are difficult to accurately control, and the application of the product has a high environmental risk. These disposal methods are essentially "pollution transfer" rather than "pollution elimination", and they fail to achieve the recycling of arsenic resources, but may trigger new environmental problems, thus largely offsetting the environmental benefits brought by phytoremediation technology and greatly reducing its economic feasibility.

[0005] To solve this problem, the arsenic-rich biomass is regarded as a "secondary resource" and high-value utilization, which has become a research hotspot in the field of environmental science and technology in recent years. Among them, the conversion of arsenic-rich biomass into biochar with pollution solidification and adsorption functions through pyrolysis technology is considered as an extremely promising and innovative approach. Pyrolysis is a process that makes biomass undergo complex cracking, dehydration, decarboxylation and polycondensation reactions under anaerobic or anoxic conditions at medium-high temperature (usually 300-800℃), ultimately generating solid-phase biochar, liquid-phase bio-oil and gas-phase pyrolysis gas. Biochar has a stable aromatic carbon skeleton structure, a developed multi-level pore system (micropore, mesopore, macropore), a large specific surface area and a rich surface oxygen-containing functional groups (such as -OH, -COOH, C=O), making it a potential high-efficiency and low-cost adsorbent. However, the original biochar obtained by pyrolysis of Pteris vittata L. is usually alkaline due to the presence of ash rich in alkali metals and alkaline earth metals on its surface, and it is usually negatively charged in water. This leads to its limited adsorption capacity for As (V) in anionic form (such as , ) in aqueous solution and neutral molecular form of As (III) (in the pH range from acidic to neutral), and even electrostatic repulsion. Therefore, Pteris vittata L. biochar must be modified to introduce specific adsorption sites with strong affinity for arsenic. Iron modification is one of the most effective and commonly used methods, which can load or post-load nanoscale iron oxides or hydroxides (such as , , This can introduce a large number of adsorption sites with extremely strong arsenic complexing ability onto the surface of biochar. It significantly enhances the arsenic removal effect through multiple mechanisms such as surface complexation, electrostatic attraction, ion exchange, and co-precipitation.

[0006] In recent years, research in related fields has provided evidence for the feasibility of this technical approach. For example, the paper "Potential in treating arsenic-contaminated water of the biochars produced from hyperaccumulator Pteris vittata and its environmental safety" systematically explored the preparation process of iron-modified Pteris vittata biochar and its removal efficiency of As(III) and As(V) in aqueous solution. This study revealed that iron loading can significantly enhance the adsorption capacity of biochar for both valence states of arsenic, and subsequent leaching experiments proved that the arsenic carried in the biochar and newly adsorbed arsenic can be stably fixed on the material, greatly reducing its environmental leaching risk. Another article, "Modeling the removal of Cd(II) and Pb(II) from aqueous solutions by biochar derived from arsenic hyperaccumulator Pteris vittata," further expanded the research scope, exploring the adsorption behavior of Pteris vittata biochar for heavy metal cations such as Cd(II) and Pb(II), and modeling the possible interactions between the inherent arsenic in the biochar and these heavy metal ions.

[0007] While the aforementioned studies have pointed the way and provided scientific evidence for the resource utilization of arsenic-rich biomass, they primarily focus on the preparation process and performance characterization of the final product (modified biochar), failing to establish a direct and quantitative link between product performance and the source of the raw material—namely, the biological characteristics of Centipede Grass in the phytoremediation process. This results in a significant "breakpoint" or "blind spot" in the existing technological system:

[0008] 1. Lack of Quality Control and Performance Evaluation of Raw Materials: When utilizing phytoremediation harvests as an industrial raw material, a scientific and unified quality evaluation standard is lacking. Centipede grass grown in different environments (e.g., soil arsenic concentration, pH, organic matter content, nutrient status), at different ages, and harvested in different seasons exhibits significant differences in arsenic accumulation levels, physiological stress states, and internal chemical components (especially secondary metabolites related to stress resistance). These differences inevitably transmit and affect the final physicochemical properties (e.g., pore structure, specific surface area) and surface chemical characteristics (e.g., type and quantity of functional groups) of the biochar prepared from it as a precursor, thus determining its adsorption performance. Without scientific performance evaluation and quality grading, it is impossible to achieve standardized and large-scale production of subsequent resource-based products, nor can its application effects in practical engineering be accurately predicted, thereby limiting the reliability and commercialization of this technology.

[0009] 2. The potential value of plant metabolomics has been overlooked: Under extreme conditions of high arsenic stress, the metabolic network of *Pteris vittata* undergoes profound adaptive restructuring to synthesize a large number of secondary metabolites to resist oxidative damage and detoxify. Existing studies have shown that *Pteris vittata* is rich in flavonoids, phenolic acids, and other phenolic secondary metabolites. These compounds possess excellent metal ion chelating ability and strong antioxidant activity, and are considered to play a crucial role in the arsenic tolerance and detoxification mechanism of *Pteris vittata*. These natural organic compounds rich in specific functional groups (such as phenolic hydroxyl groups) may act as endogenous "modifiers" during subsequent pyrolysis, with their carbon skeletons and functional groups possibly partially retained or converted into part of the surface active groups of biochar, thus having a positive, or even unexpected, synergistic enhancing effect on the adsorption performance of the final product. However, current research has not yet incorporated these indicative and potentially functional plant metabolomics characteristics into the raw material evaluation system.

[0010] Therefore, there is an urgent need in this field to develop a method that can objectively, comprehensively, and scientifically evaluate the remediation efficacy of Centipede Grass biomass for resource utilization. This method should effectively connect the actual effects of phytoremediation with the potential performance of subsequent resource-based products. Furthermore, based on this evaluation method, it is necessary to construct a new, efficient, economical, and environmentally friendly collaborative governance model for arsenic pollution in mining areas, integrating "soil remediation - efficacy evaluation - raw material classification - targeted resource utilization - wastewater treatment - water and soil reuse." Summary of the Invention

[0011] The primary objective of this invention is to overcome the shortcomings of existing technologies and provide a comprehensive method for evaluating the remedial efficacy of Centipede Grass. This method integrates core indicators of phytoremediation with metabolomics indicators reflecting its physiological state, aiming to provide a reliable quality assessment and grading standard for raw materials before resource utilization.

[0012] The second objective of this invention is to provide a specific application of the aforementioned evaluation method, namely, to construct a complete and systematic technological system for the coordinated treatment of mine water and soil pollution based on the recycling of hyperaccumulating plants. This system uses performance evaluation as the core control node, realizing a closed-loop material cycle and value chain extension from contaminated soil remediation to clean water production.

[0013] To achieve the above-mentioned objectives, this invention provides a method for evaluating the restorative efficacy of Centipede Grass, which includes, but is not limited to, the following core steps:

[0014] Step A: Standardized sample collection and pretreatment:

[0015] After the pre-set phytoremediation cycle, following statistical principles, the above-ground harvestable portions of mature *Pteris vittata* plants were randomly and representatively collected from multiple locations on the target remediation site. The collected plant samples were repeatedly rinsed and washed with deionized water to thoroughly remove surface dust, soil particles, and other exogenous contaminants. The samples were then placed in a constant-temperature forced-air drying oven and dried to constant weight at 60-65℃ to obtain a stable dry weight baseline. The completely dried samples were then finely pulverized using a high-speed plant pulverizer, and the resulting powder was passed through a 100-mesh standard sieve to obtain uniform particle size and composition. This powder was then stored in a sealed desiccator for later use.

[0016] Step B: Precise testing of core and auxiliary evaluation indicators:

[0017] Accurate quantitative analysis of the following two types of core evaluation indicators was performed on the standardized pretreated sample powder:

[0018] B1. Core indicators of phytoremediation efficacy: Total arsenic (As) concentration in aboveground parts ( Determination of )

[0019] This indicator directly quantifies the total amount of arsenic extracted from the soil and transported to the aboveground parts of Centipede Grass. The preferred method for determination is microwave digestion-inductively coupled plasma mass spectrometry (ICP-MS), which offers extremely high sensitivity and accuracy. Alternatively, microwave digestion-atomic fluorescence spectrometry (MA / AFS) can be used under specific conditions. The specific operating procedure is as follows: Accurately weigh a certain amount of homogeneous sample powder into a clean polytetrafluoroethylene digestion vessel, and add sufficient analytical grade nitric acid (…). ) and hydrogen peroxide ( The mixture was digested using a multi-stage temperature-pressure microwave digestion program. After cooling, the digest was carefully and quantitatively transferred to a clean volumetric flask and diluted to the designated mark with ultrapure water. Finally, the total arsenic concentration in the solution was determined using a calibrated ICP-MS or AFS, and the total arsenic concentration in the dry weight of the centipede grass was accurately calculated based on the original sample mass and the final volume. .

[0020] B2. Auxiliary indicators of plant physiological health: Determination of key secondary metabolite concentrations

[0021] This indicator reflects the physiological stress response intensity and health status of *Pteris vittata* under arsenic stress. Specific secondary metabolites (such as flavonoids) enriched in the plant are not only markers of its stress resistance but may also have a positive potential impact on the surface chemistry and adsorption performance of the subsequently prepared biochar. This invention uses the total flavonoid concentration (… The following are representative auxiliary indicators for explanation. High-performance liquid chromatography (HPLC) with high resolution and quantitative accuracy is recommended for the determination method, or ultrasound-assisted extraction-ultraviolet-visible spectrophotometry (UAE-UV-Vis) for rapid screening.

[0022] Taking HPLC as an example: A certain amount of sample powder is accurately weighed, and a specified volume of extraction solvent is added. High-efficiency ultrasonic-assisted extraction is performed in an ultrasonic cleaner with temperature control. After purification by high-speed centrifugation and filtration through a 0.22 μm microporous membrane, the extract is injected into the HPLC system for analysis. Chromatographic conditions can be set as follows: C18 reversed-phase column; gradient elution program of methanol-0.1% phosphoric acid aqueous solution as the mobile phase; diode array detector (DAD) to monitor the characteristic absorption wavelengths of flavonoids. A standard curve is prepared using one or more representative flavonoids (such as rutin and quercetin) as external standards. The content of total flavonoids or specific flavonoids in the sample is accurately quantified using the external standard method, and the total flavonoid concentration in the dry weight of *Centipeda minima* is calculated. .

[0023] Step C: Establish a comprehensive remediation effectiveness evaluation system and classify raw materials:

[0024] Based on the measured primary and secondary evaluation indicators, a quantitative evaluation index that can comprehensively reflect the restorative efficacy of Centipede Grass is established. In this invention, it is called the Comprehensive Evaluation Index of Restorative Efficacy. Based on this index, each batch of harvested Centipede Grass biomass is scientifically and objectively graded.

[0025] The EEI can be calculated using a weighted summation model:

[0026] ;

[0027] in:

[0028] and These are the weighting coefficients for the primary indicator (core indicator of remediation efficacy) and the auxiliary indicator (auxiliary indicator of physiological health), respectively, with a sum of 1. Based on the crucial importance of arsenic accumulation in phytoremediation and resource utilization, the weighting allocation should reflect its dominant position, and can be set as follows: .

[0029] and These are the preset reference maximum or ideal value of each indicator, or the value obtained through statistical analysis of a large amount of preliminary experimental data.

[0030] Based on the calculated EEI value, the harvested centipede grass biomass is clearly graded into the following three grades:

[0031] High-efficiency remediation grade (primary raw material): EEI ≥ 0.8. This rating indicates that this batch of Centipede Grass not only has extremely high arsenic enrichment efficiency, but also exhibits healthy physiological conditions and strong stress resistance. This type of raw material is the best choice for preparing top-grade special arsenic removal biochar with maximum adsorption capacity and optimal kinetic performance.

[0032] Qualified remediation grade (secondary raw material): 0.5≤EEI <0.8. This rating indicates that this batch of Centipede Grass has good or relatively good arsenic accumulation capacity and acceptable physiological state, which can meet the requirements of conventional resource utilization. It is the main raw material for large-scale production of general-purpose arsenic removal biochar that meets national or industry standard performance indicators.

[0033] Poor Performance Grade (Substandard Raw Material): EEI <0.5. This rating indicates that the batch of Centipede Grass has poor remediation effect, low arsenic accumulation, or the plants are in a state of severe stress and decay. Its economic value and technical feasibility for resource utilization are both low. This type of raw material should be excluded from the resource utilization process, and other environmentally friendly and harmless disposal methods are recommended.

[0034] This invention further provides a specific application of the above-mentioned remediation effectiveness evaluation method, namely, constructing a systematic method for the coordinated remediation of mine water and soil pollution based on the recycling of hyperaccumulating plants. This application method strictly adheres to the scientific principle of "evaluation before application," using the established effectiveness evaluation system as an indispensable key quality control link connecting upstream soil remediation and downstream resource utilization. Its specific implementation process is as follows:

[0035] The first step in the application process: raw material production and efficacy evaluation based on phytoremediation.

[0036] This step corresponds entirely to the performance evaluation method described above. First, on the planned arsenic-contaminated soil in the mining area, after necessary engineering measures, large-scale planting of *Pteris vittata* is carried out. After one or more growth cycles, a unified harvest is conducted. Subsequently, strictly following the aforementioned sampling and testing procedures, all the *Pteris vittata* biomass harvested in this batch is sampled and tested, its EEI value is calculated, and quality assessment and grading are completed based on this value.

[0037] The second step in the application process: targeted resource utilization of high-quality raw materials based on evaluation results.

[0038] Only centipede grass biomass evaluated as "high-efficiency remediation grade (primary raw material)" or "qualified remediation grade (secondary raw material)" is eligible to enter this resource utilization process. This process aims to efficiently and stably prepare high-performance, highly safe iron-modified biochar adsorbents.

[0039] 1. Initial biochar preparation: Graded high-quality centipede grass powder is placed in an industrial-grade pyrolysis device under an inert atmosphere (such as high-purity nitrogen or flue gas) for primary pyrolysis. After the material is cooled to room temperature by a cooling system, porous initial biochar is obtained.

[0040] 2. Iron-modified loading: Iron phase loading was performed using a stable and easily scalable chemical coprecipitation method. First, according to... The molar ratio is precisely 2:1, using stoichiometric amounts of ferric chloride hexahydrate ( ) and ferrous sulfate heptahydrate ( The initial biochar obtained from primary pyrolysis is dissolved in ultrapure water to prepare a mixed solution of iron salts of the desired concentration. Then, the initial biochar is dispersed in this solution at a predetermined solid-liquid ratio, with the total molar ratio of carbon to iron (C:Fe) in the biochar controlled between 1:0.05 and 1:0.1. Under continuous and uniform mechanical stirring, a high-concentration NaOH solution is slowly added dropwise using an automatic titration system to precisely adjust and stabilize the pH of the system within the range of 9.5-10.5. At this point, co-precipitation of ferrous and ferric ions occurs, forming a black magnetic... Nanoparticles are deposited on the inner and outer surfaces of biochar.

[0041] 3. Precipitation ripening and secondary pyrolysis: Under an inert atmosphere, the above liquid is heated to 75-85℃ and reacted (ripened) at this temperature for 1-2 hours to promote precipitation. The growth of nanocrystals enhances their crystallinity and strengthens their bond with the biochar support. After the reaction, the solid product is separated by pressure filtration or centrifugation. The solid is washed several times with alternating amounts of distilled water and anhydrous ethanol until the washing solution is neutral and its conductivity is close to that of pure water, to thoroughly remove residual unreacted ions and byproduct salts. The washed solid is then thoroughly dried at 80°C. The dried iron-modified biochar undergoes a secondary low-temperature pyrolysis treatment, with the temperature slowly increased at a rate of 2-5°C / min to 280-320°C and held at this temperature for 1 hour. This step aims to further stabilize the iron oxide phase, remove unstable organic functional groups from the material, and further optimize the pore structure of the biochar, thereby increasing its specific surface area.

[0042] 4. Finished product processing: After cooling, necessary re-cleaning and drying, the product after secondary pyrolysis can be crushed and sieved according to application requirements to obtain high-performance, high-safety iron-modified centipede grass biochar adsorbent with a specific particle size range, and then sealed and packaged.

[0043] The third step in the application process: the application of modified biochar in the treatment of arsenic-containing wastewater.

[0044] The iron-modified biochar prepared in the previous step is used as a highly efficient adsorbent to treat acidic or neutral arsenic-containing wastewater from the mining area. Based on the wastewater volume, initial arsenic concentration, pH value, and coexisting ion composition, the optimal dosage and optimal operating pH range of the biochar are determined through small-scale or pilot-scale laboratory experiments. The biochar is placed in the reactor by addition or filling, ensuring thorough mixing and contact with the wastewater. Sufficient mass transfer kinetics are provided through mechanical stirring or aeration to ensure efficient adsorption. The adsorption contact time is determined based on adsorption kinetics experimental results, typically not less than several hours, to ensure adsorption equilibrium is reached or effluent quality standards are met.

[0045] The fourth step in the application process: system closed loop and sustainable operation.

[0046] After adsorption treatment, the wastewater undergoes further solid-liquid separation (such as sedimentation tanks and filters), resulting in significantly improved water quality and a substantial reduction in arsenic concentration, meeting relevant national discharge or reuse standards. The treated water can be reused on-site as a valuable reclaimed water resource. For example, it can be used for irrigation of remediated mining soil to maintain ecosystem health, for dust suppression on mining roads to improve air quality, or as supplementary water for industrial processes such as mineral processing, thereby greatly reducing the consumption of fresh water resources in the region and achieving water resource recycling. The arsenic in the saturated biochar has a very low risk of environmental leaching because the arsenic it contains is stabilized by iron oxides through strong chemical bonds. This type of safe saturated adsorbent can be considered as an additive or aggregate in low-value building materials for final resource recovery, thus achieving the "termination" and "solidification" of pollutants. Therefore, this invention constructs a complete, closed-loop, and sustainable material cycle and pollution synergistic treatment system, from "contaminated soil" to "arsenic-rich plants," then to "highly efficient adsorbents," and finally back to "clean water" and "healthy land." Detailed Implementation

[0047] To ensure that the technical objectives, solutions, and advantages of this invention are more clearly and completely understood and realized by those skilled in the art, the technical solutions of this invention will be described in detail and without limitation below in conjunction with preferred specific embodiments. It should be emphasized that the following description is a preferred example among the many feasible embodiments of this invention, intended to illustrate the core technical ideas and specific operational processes of this invention, and not to limit the scope of protection of this invention in any way. Any simple modifications, equivalent substitutions, combinations, or improvements made by those skilled in the art to the following embodiments without departing from the core spirit and technical essence of this invention should be included within the scope of protection of this invention.

[0048] Part 1: Specific Implementation of the Evaluation Method for the Restorative Efficacy of Centipede Grass

[0049] This section details a complete experimental procedure to scientifically, rigorously, and reproducibly evaluate the remediation efficacy of centipede grass biomass harvested through phytoremediation for resource utilization.

[0050] 1. Standardized sample collection and pretreatment procedures:

[0051] To ensure the accuracy, reliability, and comparability of evaluation results across different batches, every step of sample collection and pretreatment must strictly adhere to standardized operating procedures.

[0052] 1.1 Collection Timing and Representative Sampling Strategy:

[0053] Timing of Collection: Collection should be carried out at the end of the centipede grass's growth cycle, when the plant biomass and the accumulation of pollutants within it theoretically reach their peak. The specific timing needs to be determined based on local climate conditions and the phenological stage of centipede grass, generally at the end of the local growing season, before the plant begins to show partial yellowing but has not completely withered. Generally speaking, in temperate or subtropical regions, 6 to 12 months after planting is the most suitable window for harvesting and sampling.

[0054] Sampling Strategy: For a remediation plot to be evaluated or a batch of harvested material, to eliminate bias caused by spatial heterogeneity, a "multi-point pooled sampling method" must be used to obtain samples with sufficient statistical representativeness. An "S"-shaped or "checkerboard" sampling method can be used, randomly but evenly setting a sufficient number of sampling points within the plot. The number of sampling points should not be less than 15, and should be increased accordingly for large plots. At each selected sampling point, randomly select 3-5 representative *Pteris vittata* plants of moderate growth condition.

[0055] Sample location and collection procedure: The target sample should be the economically harvestable above-ground portion of *Pteris vittata*, specifically, about 2-3 cm above the base of the rhizome. Use clean stainless steel scissors to cut all the pinnate leaves. Tools used during collection must be kept clean. After collecting samples from each plot, wash with deionized water and dry with lint-free paper to prevent cross-contamination. Collected samples should be immediately placed in pre-labeled, clean polyethylene sample bags. The label should include the plot number, sampling point coordinates, sampling date, and the collector's information.

[0056] 1.2 Fine cleaning and deactivation drying of samples:

[0057] Cleaning: After collecting all leaf samples from the same plot, a three-step cleaning method was performed. First, rinse under running tap water to remove large pieces of soil and surface deposits. Second, immerse the samples in a large container filled with deionized water and gently brush both sides of the leaves with a clean, soft brush, paying particular attention to the veins and folds. Third, rinse repeatedly with deionized water 3-5 times until the water is clear and free of any visible impurities. This step is crucial for eliminating interference from exogenous arsenic contamination in subsequent elemental analysis.

[0058] Drying and Enzyme Inactivation: Place the cleaned sample on a clean, rust-free tray, drain excess water, and then quickly place it into a preheated constant-temperature drying oven. First, perform a blanching treatment at a relatively high temperature of 105℃ for 15-20 minutes. The purpose is to rapidly inactivate the activity of various enzymes in the plant (such as polyphenol oxidase and peroxidase), preventing the oxidation or degradation of secondary metabolites (such as flavonoids) during the subsequent slow drying process, thus preserving the original chemical composition of the sample. After blanching, lower the oven temperature to 60℃, turn on the forced-air drying function, and continuously dry the sample until it reaches constant weight. The criterion for constant weight is: the weight change of the sample is less than 0.1% of its total weight in two consecutive weighings (2 hours apart). This process usually takes 48-72 hours.

[0059] 1.3 Sample crushing, sieving, and homogenization:

[0060] Grinding and Sieving: Thoroughly grind the completely dried centipede grass sample using a high-speed multi-functional grinder (such as a grinder with a stainless steel inner liner and blades). To ensure sample homogeneity and reaction sufficiency for subsequent chemical analysis, the ground sample must be sieved through a standard analytical sieve. For samples used for core indicator analysis, it is recommended that all samples pass through a 100-mesh nylon sieve. Any material remaining on the sieve should be returned to the grinder for further grinding until all material passes through.

[0061] Homogenization: Collect all the sieved powders on clean, smooth cellophane or kraft paper, and mix them thoroughly using the "quartering method" or repeated diagonal folding method, mixing at least 20 times to ensure that the final sample powder has the same chemical composition in any tiny part.

[0062] Storage: Finally, aliquot the highly homogenized sample powder into clean, dry, and clearly labeled brown wide-mouth glass vials with sealed caps. Place the vials in a glass desiccator containing silica gel as a desiccant and store at room temperature, away from light, for later use.

[0063] 2. Precise measurement procedures for core and auxiliary evaluation indicators:

[0064] 2.1 Main performance indicator: Total arsenic concentration in aboveground parts ( Determination of )

[0065] Digestion Method: A microwave-assisted acid digestion method with high efficiency, low pollution, and good recovery rate is employed. Accurately weigh 0.1500 g (accurate to 0.1 mg) of homogeneous sample powder and carefully transfer it into a clean, dry polytetrafluoroethylene (PTFE) or modified Teflon (TFM) microwave digestion vessel. Slowly add 5.0 mL of analytical grade (MOS grade or higher) concentrated nitric acid to the vessel. 65-68%) and 1.0 mL of superior grade hydrogen peroxide ( (30%). After closing the inner cap and tightening the outer cap, let it stand for 15 minutes to allow the sample to be initially wetted and reacted with the acid solution, in order to prevent the reaction from being too violent when the temperature is increased later. In the same batch of experiments, at least two sets of method blank controls (without sample, only the same volume of acid solution) and one set of certified standard reference material must be prepared simultaneously for quality control and result confirmation throughout the process.

[0066] Microwave digestion program: Place all digestion vessels (including samples, blanks, and standards) symmetrically on the microwave digester turntable, and set and run an optimized multi-stage temperature-pressure holding program. A typical program can be set as follows:

[0067] 1. Heating stage 1: Within 10 minutes, the power linearly increases to 1600W, bringing the temperature inside the tank to 120℃.

[0068] 2. Heat preservation stage 1: Maintain at 120℃ for 5 minutes.

[0069] 3. Heating Phase 2: Within 10 minutes, the temperature continues to climb to 180℃.

[0070] 4. Heat preservation stage 2: Maintain stable pressure and temperature at 180℃ and continue the reaction for 20 minutes.

[0071] 5. Cooling stage: After the program is completed, start the instrument’s built-in air cooling system to force-cool the digestion vessel until the pressure inside the vessel drops to a safe range (usually below 0.2 MPa).

[0072] Volume Adjustment and Analytical Preparation: After the digestion vessel has completely cooled to room temperature, carefully open it in a fume hood. Visually inspect the digestion solution; it should be a completely clear, transparent, colorless or pale yellow solution. If the solution still contains small particles or is darker in color, place the digestion vessel (without the inner lid) on a 120°C hot plate to remove the acid until approximately 1 mL of liquid remains. After cooling, repeat the acid addition and microwave digestion. Carefully and repeatedly wash the inner wall and inner lid of the digestion vessel with ultrapure water (resistivity ≥18.2 MΩ·cm) in small batches. Transfer all washings to a 25.00 mL or 50.00 mL Grade A polypropylene volumetric flask. Finally, dilute to the mark with ultrapure water, stopper the flask, and invert to mix well.

[0073] Instrumental analysis (ICP-MS): Total arsenic was determined using a well-tuned inductively coupled plasma mass spectrometer. Optimized instrument parameters included: RF power ~1550W, plasma gas flow rate ~15 L / min, auxiliary gas flow rate ~0.9 L / min, and carrier gas flow rate ~1.0 L / min. The most important isotope of arsenic was selected. Detection should be performed. To correct for complex plant matrix effects and instrument signal drift, a multi-element mixed internal standard solution (such as one containing...) should be used, either by online addition or offline mixing. Prepare a standard curve by configuring a series of arsenic single-element standard solutions with concentration gradients (e.g., 0, 1, 5, 10, 25, 50, 100 μg / L), and require a linear correlation coefficient. Not less than 0.999. The sample solution, blank solution, and standard reference solution were analyzed according to a predetermined sequence, with each sample measured three times and the average value taken.

[0074] Data Processing and Quality Assurance: Based on the signal intensity and standard curve equation, the arsenic concentration in the sample dilution was calculated. Then, the total arsenic concentration in the dry weight of *Centipeda minima* was calculated using the following formula. :

[0075]

[0076] in, The average concentration (μg / L) of the sample solution was measured. The average concentration (μg / L) was measured for the blank solution. The constant volume (L) Diluting factor The sample dry weight (kg) is used. Simultaneously, the recovery rate of the standard reference material is calculated, and the result should fall within the acceptable range of 85%-115% of the certified value; otherwise, the experimental data for that batch is invalid and must be repeated.

[0077] 2.2 Auxiliary efficacy indicators: Total flavonoid concentration ( Determination of )

[0078] Extraction method: A highly efficient and environmentally friendly ultrasonic-assisted solvent extraction method was employed. 0.5000 g of homogeneous sample powder was accurately weighed into a 50 mL stoppered conical flask, and 25.0 mL of chromatographically pure 80% (v / v) methanol aqueous solution was precisely added. The conical flask was placed in a CNC-controlled constant-temperature ultrasonic water bath, with the ultrasonic frequency set to 40 kHz, ultrasonic power to 250 W, and the water bath temperature maintained at 50 °C. After tightly sealing the flask, extraction was continued for 40 minutes.

[0079] Sample purification: After extraction, centrifuge the extract at 12,000 rpm (or approximately 13,800 x g) for 15 minutes at 4°C to precipitate fine insoluble matter. Carefully aspirate the supernatant and pass it through a 0.22 μm pore size polytetrafluoroethylene (PTFE) or nylon syringe filter. Inject the filtrate into a 2 mL HPLC sample vial, seal the vial, and proceed with analysis.

[0080] HPLC analysis conditions: Use a high-performance liquid chromatography system equipped with a diode array detector (DAD) or ultraviolet-visible detector (UVD).

[0081] Chromatographic column: High-performance reversed-phase C18 column was selected.

[0082] Mobile phase: Phase A was 0.1% (v / v) aqueous phosphoric acid solution (prepared with HPLC-grade phosphoric acid and ultrapure water), and Phase B was chromatographically pure methanol. A gradient elution program was used, and an optimized gradient example is as follows: 0-10 min, 10-30% B; 10-40 min, 30-70% B; 40-45 min, 70-10% B; 45-50 min, 10% B (column equilibration).

[0083] Operating parameters: mobile phase flow rate 1.0 mL / min, column oven temperature maintained at 30℃, injection volume 10 μL.

[0084] Detection: The DAD detector is set to scan the full wavelength range of 200-400 nm to obtain complete spectral information and extract two characteristic absorption wavelengths of flavonoids: strong absorption of flavonols at about 360 nm and strong absorption of isoflavones and flavanones at about 254 nm, for quantitative and qualitative analysis.

[0085] Quantitative analysis and data processing: High-purity (≥98%) rutin or quercetin was used as an external standard. A series of standard solutions with concentration gradients (e.g., 10, 25, 50, 100, 200 mg / L) were precisely prepared and analyzed under the same chromatographic conditions as the samples. A standard curve was plotted as peak area versus concentration. ≥0.999. Based on the sum of the peak areas of the major flavonoids at corresponding retention times in the sample chromatogram, substitute them into the standard curve equation to calculate the concentration of total flavonoids in the extract. Finally, convert this to the total flavonoid concentration in the dry weight of *Centipeda minima* using the following formula. (in rutin or quercetin equivalents):

[0086]

[0087] in, The concentration of the extract (mg / L) is read from the standard curve. The extraction solvent volume (L) The dry weight of the sample is (g).

[0088] 3. Construction and tiered implementation of a repair effectiveness evaluation system:

[0089] 3.1 Construction and Optimization of the Overall Evaluation Index (EEI):

[0090] Model Construction: As described in the invention, a weighted model is constructed. Determining the weight coefficients is a crucial step. Besides initial setting based on expert scoring or the Analytic Hierarchy Process (AHP), a more scientific method is correlation analysis. That is, through extensive experiments, the final arsenic removal performance (such as maximum adsorption capacity) of iron-modified biochar prepared from centipede grass raw materials with different EEI values ​​is systematically studied. Adsorption rate constant (etc.), to establish a statistical correlation model between EEI values ​​and final product performance indicators. Through methods such as multiple linear regression, the weighting coefficients can be optimized in reverse. and This allows for maximum prediction of the final product's performance.

[0091] Determination of the reference maximum value: The reference maximum value used for normalization and The value of this value is crucial to the stability and rationality of the evaluation results. After conducting a comprehensive survey and statistical analysis of a large number of centipede grass samples from different sources, under different growth conditions, and with different growth years, it is not advisable to take the extreme maximum value. Instead, the 95th percentile value of its statistical distribution or a generally accepted ideal target value should be taken to ensure the robustness and universality of the evaluation system.

[0092] 3.2 Quality Classification and Differentiated Application Decisions

[0093] Based on the calculated EEI value, a clear quality grading and subsequent processing path decision are made for each batch of centipede grass harvest.

[0094] High-efficiency remediation grade (primary feedstock, EEI ≥ 0.8): This type of feedstock has extremely high arsenic content and strong physiological activity, and is considered a "premium grade." It should be given priority for preparing top-grade, high-value-added specialty arsenic removal biochar. For example, more refined pore size control techniques (such as combined template agent methods) or secondary functionalization modifications (such as loading other metal / non-metal elements with adsorption or catalytic functions) can be used to pursue ultimate adsorption performance and meet the special wastewater treatment needs with extremely high effluent quality requirements.

[0095] Qualified remediation grade (secondary raw material, 0.5≤EEI <0.8): This type of raw material exhibits good arsenic enrichment and acceptable physiological conditions, and is considered "qualified." It is suitable for large-scale, standardized production processes to prepare arsenic-removing biochar that meets general standard performance indicators. This is the main raw material for the future large-scale industrial application of this technology, and efforts should be focused on optimizing the cost-effectiveness of its production process.

[0096] Poor performance grade (unqualified raw materials, EEI <0.5): These raw materials have low remediation efficiency or poor physiological condition, and do not have economic value for resource utilization; they are "unqualified products." They should be resolutely removed from the resource utilization process, and other environmentally friendly harmless disposal technologies are recommended. For example, pyrolysis carbonization under strict control of flue gas emissions to maximize the stabilization of arsenic, or mixing with other inert materials (such as cement and fly ash) for solidification / stabilization treatment before final disposal in a designated hazardous waste secure landfill.

[0097] The following details how the established remediation effectiveness evaluation method can be used as the core technical node and quality control checkpoint of the system, and applied to a complete, logically closed-loop collaborative governance system for arsenic pollution in soil and water in mining areas.

[0098] 1. System process design and integrated operation:

[0099] The system strictly follows a closed-loop logic of "soil purification → plant harvesting → performance evaluation → raw material diversion → targeted preparation → wastewater treatment → resource reuse", forming a highly efficient industrial chain.

[0100] 1.1 Soil Remediation and High-Quality Raw Material Production: Implement a phytoremediation project using *Pteris vittata* (centipede grass) on large areas of arsenic-contaminated land in the target mining area. The core objective of this stage is not only to remediate the soil, but also to act as an "upstream workshop" to produce as much high-EEI value *Pteris vittata* biomass as possible for the downstream resource utilization plant. Implementable agronomic enhancement measures include: applying phosphate fertilizer to promote plant growth, but controlling the amount to avoid competition with arsenate for absorption sites; applying soil conditioners (such as lime and organic fertilizer) to adjust the soil pH to slightly acidic (6.0-6.5), a pH range conducive to *Pteris vittata* growth and arsenic bioavailability; and, under specific conditions, cautiously applying low concentrations of chemical chelating agents (such as EDTA) or biosurfactants to temporarily activate fixed arsenic in the soil.

[0101] 1.2 Performance Evaluation and Intelligent Raw Material Diversion: The performance evaluation methods described in Part 1 are strictly followed. Each batch and each plot of harvest must undergo sampling, testing, EEI value calculation, and grading. In modern processing centers, this process is automated: automated sampling systems, analytical instruments networked with a LIMS (Laboratory Information Management System), and software that automatically calculates the EEI and provides grading results. Based on the evaluation results, the raw materials are transported to different storage bins or processing lines, achieving intelligent diversion.

[0102] 1.3 Targeted and large-scale preparation of iron-modified biochar based on evaluation results:

[0103] Process selection and fine-tuning: The preparation process is refined and differentiated according to the grade of raw materials. For example, for primary raw materials, a higher pyrolysis temperature can be used to obtain a larger specific surface area, or the iron loading can be increased to provide more adsorption sites. For secondary raw materials, a standard production process optimized through cost-benefit analysis is adopted.

[0104] Detailed description of large-scale production process:

[0105] 1. Primary Pyrolysis: Qualified centipede grass powder is continuously fed into a large industrial rotary kiln or multi-layer belt pyrolysis furnace via a screw feeder. Nitrogen generated by a nitrogen generator or purified, deoxygenated boiler flue gas is introduced into the furnace as a protective inert atmosphere. The temperature distribution in each section of the furnace is precisely controlled by a PLC system to achieve programmed heating (heating rate 10℃ / min). The final residence time of the material in the high-temperature zone (500℃) is precisely controlled by adjusting the rotation speed of the rotary kiln or the speed of the conveyor belt (30 minutes). The biochar produced by pyrolysis is collected after cooling via a water-cooled screw feeder.

[0106] 2. Iron Modification: After cooling, the initial biochar produced by pyrolysis is fed into a large stainless steel reactor equipped with a powerful stirring device and a temperature control jacket. Iron is then pumped into pre-prepared feedstock in calculated proportions using metering pumps. A mixed solution and a NaOH solution were prepared. The pH value of the slurry in the reactor was monitored in real time by an online high-precision pH electrode linked to a PLC, precisely controlling the dripping rate of NaOH to stabilize the pH at the final reaction point at 10. Subsequently, steam or heat transfer oil was introduced into the reactor jacket to raise the temperature inside the reactor and maintain it at 80°C for a aging reaction for 1 hour.

[0107] 3. Secondary pyrolysis and activation: After precipitation, the slurry undergoes solid-liquid separation and preliminary dewatering using a plate and frame filter press. The resulting filter cake is then fed into a similarly structured pyrolysis furnace for secondary low-temperature pyrolysis at 300°C. This process not only stabilizes the iron phase but also utilizes the small amount of reducing gas generated during pyrolysis to slightly activate the biochar, further clearing and optimizing its pore structure.

[0108] 4. Post-processing and finished product: The final product is cooled, crushed (e.g., using a hammer crusher) and screened (e.g., using a vibrating screen to screen to a specific particle size range, such as 20-40 mesh, to adapt to different reactor types), and then dusted by an air separation system. Finally, it is weighed and packaged by an automatic packaging machine to become the finished iron-modified biochar adsorbent.

[0109] 1.4 High-efficiency application of modified biochar in wastewater treatment:

[0110] Reactor type: Different types of reactors can be flexibly selected based on the treatment scale and wastewater characteristics. For small-batch, intermittent wastewater, a stirred tank reactor (CSTR) can be used for batch treatment. For large-flow, continuous wastewater, fixed-bed or fluidized-bed reactors are preferred for continuous flow treatment, which is more efficient and saves space.

[0111] Operating parameter optimization and operation monitoring: Before formal commissioning, optimal operating parameters must be determined through a series of laboratory-scale batch and continuous flow experiments.

[0112] Dosage / bed height: The amount of biochar required per unit volume of wastewater or the minimum bed height required for a fixed bed is determined by adsorption isotherm experiments.

[0113] pH adjustment: Before entering the adsorption unit, arsenic-containing wastewater may need to be pre-adjusted to the optimal adsorption range of 5.0-6.5 by adding acid or alkali.

[0114] Contact time / empty bed residence time: The shortest contact time or hydraulic residence time required to achieve the treatment target is determined through adsorption kinetic experiments (such as fitting pseudo-first-order and pseudo-second-order kinetic models) or fixed-bed breakthrough curve experiments.

[0115] Operational Monitoring: In continuous treatment systems, online water quality analysis instruments must be installed at the effluent outlet to monitor the arsenic concentration, pH, and turbidity in the effluent in real time, ensuring that the effluent quality consistently meets standards. When the arsenic concentration in the effluent approaches the warning line, the system will automatically alarm, prompting the need to replace or regenerate the adsorbent material.

[0116] 1.5 System Closed-Loop and Sustainability Management:

[0117] Water reuse: After treatment, the water must undergo water quality testing to confirm that it meets the corresponding reuse standards. Priority will be given to reusing it for vegetation maintenance in restored areas to form a virtuous cycle of "water-soil-plants", or supplying it for mining production (such as ore dressing and coal washing) and domestic miscellaneous uses, so as to achieve efficient internal circulation of water resources and minimize the pressure on the external water environment.

[0118] Final safe disposal of saturated adsorbents: For saturated biochar, a rigorous environmental safety assessment must be conducted, the core of which is a toxicity leaching test, such as the standard "Identification Standard for Hazardous Waste: Leaching Toxicity Identification". If the assessment results indicate that the arsenic it contains has been stably fixed in the biochar-iron oxide composite, and the arsenic concentration in the leachate is far below the limit of the hazardous waste identification standard, then it can be considered environmentally safe. This type of material can be used as a functional aggregate, incorporated into cement, concrete, sintered bricks, or roadbed materials for resource utilization, achieving the final solidification, stabilization, and safe disposal of pollutants.

[0119] Through the detailed implementation methods described above, this invention provides a complete and operable technical system. It not only innovatively proposes a method for scientifically evaluating the remediation efficacy of centipede grass and solves the problem of raw material standardization, but more importantly, it organically connects multiple previously isolated technical links to construct a new environmentally friendly and economically feasible pollution control and resource recycling model, providing technical support for the ecological restoration and sustainable development of heavily arsenic-polluted areas such as mining areas.

Claims

1. A method for evaluating the restorative efficacy of Centipede Grass, characterized in that, Includes the following steps: a) Collect and preprocess the above-ground parts of the centipede grass to obtain a homogeneous dry powder sample; b) Detect the total arsenic concentration in the aboveground parts of the dry powder sample, which is a core indicator of remediation efficacy. ); c) Detect the total flavonoid concentration in the dry powder sample as a physiological health auxiliary indicator ( ); d) Construct the comprehensive evaluation index of repair effectiveness (EEI), the calculation formula of which is: ； in, and These are the weighting coefficients. and ; and This is the preset normalized reference maximum value; e) Based on the calculated EEI value, the biomass of Centipede Grass is classified into efficiency levels to guide whether it should be used for resource recovery or harmless disposal.

2. The evaluation method according to claim 1, characterized in that, The total arsenic concentration mentioned in step b) The detection of total flavonoids was performed using microwave digestion-inductively coupled plasma mass spectrometry (ICP-MS) or microwave digestion-atomic fluorescence spectrometry (AFS); the total flavonoid concentration mentioned in step c) The detection of ) was performed using high performance liquid chromatography (HPLC) or ultrasound-assisted extraction-UV-Vis spectrophotometry.

3. The evaluation method according to claim 1, characterized in that, The weighting coefficients mentioned in step d) are set as follows: , The effectiveness grading criteria mentioned in step e) are as follows: EEI ≥ 0.8 is the high-efficiency repair level, 0.5 ≤ EEI < 0.8 is the qualified repair level, and EEI < 0.5 is the poor-efficiency level.

4. An application method based on the evaluation method according to any one of claims 1 to 3, characterized in that, A mine water and soil pollution co-treatment system was constructed, which includes: a) Raw material production and efficiency evaluation unit: Centipede grass is planted and harvested on arsenic-contaminated soil, and the efficiency of the harvested biomass is evaluated and graded using the evaluation method described above. b) Targeted resource utilization unit: Centipede grass biomass evaluated as high-efficiency remediation grade or qualified remediation grade is prepared into iron-modified biochar adsorbent; c) Wastewater treatment unit: The iron-modified biochar adsorbent is applied to the purification treatment of arsenic-containing wastewater; d) System closed-loop unit: The treated wastewater that meets the standards is reused, and the saturated biochar is safely disposed of or reused.

5. The application according to claim 4, characterized in that, Methods for preparing iron-modified biochar adsorbents in targeted resource recovery units include: a) Primary pyrolysis: The qualified centipede grass powder is pyrolyzed at 450-550℃ under an inert atmosphere to obtain initial biochar. b) Iron-modified loading: Iron oxide (Fe3O4) was loaded onto the initial biochar using a chemical co-precipitation method. ); c) Secondary pyrolysis: The biochar loaded with iron oxides is subjected to secondary pyrolysis at 280-320℃ to obtain the final iron-modified biochar adsorbent.

6. The application method according to claim 5, characterized in that, In the iron-modified loading step, the chemical coprecipitation method specifically involves dispersing the initial biochar in a medium containing... and In the mixed solution, and The molar ratio is 2:1, and then an alkaline solution is added dropwise to adjust the pH of the system to 9.5-10.5, and the ripening reaction is carried out at 75-85℃.

7. The application method according to claim 4, characterized in that, In the wastewater treatment unit, iron-modified biochar adsorbent is added to arsenic-containing wastewater, and the pH value of the wastewater is adjusted to the optimal adsorption range of 5.0-6.

5. The adsorbent is then brought into full contact with the wastewater through stirring or fluidization until the arsenic concentration in the effluent reaches the preset standard.

8. The application method according to claim 4, characterized in that, In the closed-loop unit of the system, the adsorbed biochar is evaluated by toxicity leaching test to confirm its environmental safety, and then it is used as an additive in building materials for resource utilization.

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