A method for evaluating long-term release risk of heavy metals in biochar by simulating rhizosphere environment

Abstract

This invention discloses a method for simulating the rhizosphere environment to assess the long-term release risk of heavy metals from biochar. The method includes: first, culturing homologous biochar samples in natural soil to obtain a baseline value W0 for the release ratio of the target heavy metal; and simultaneously conducting a standardized accelerated aging experiment with an organic acid solution, determining the organic acid aging time t required to reach W0 by comparison. eq This invention establishes a quantitative conversion relationship between "organic acid aging time" and "natural aging time." Subsequently, the same accelerated aging experiment is performed on the biochar under test. Using the aforementioned quantitative relationship, the organic acid aging time is converted into an equivalent natural aging time, and a long-term release kinetic prediction model is constructed. Ultimately, this allows for rapid and quantitative prediction of the cumulative release ratio of heavy metals after the target age. This invention provides an efficient and reliable tool for evaluating the long-term chemical oxidation stability of biochar.

Description

Technical Field

[0001] This invention relates to the field of environmental risk assessment technology, and in particular to a method for simulating the rhizosphere environment to assess the long-term release risk of heavy metals from biochar. Background Technology

[0002] Currently, biochar, as an excellent soil conditioner, has attracted much attention due to its environmental safety. Biochar derived from raw materials such as sludge and livestock manure often contains endogenous heavy metals. Whether these heavy metals will continue to be released during the decades-long field aging process is the core of assessing its long-term environmental risk. Traditional long-term risk assessments rely entirely on soil incubation experiments that take several years, which is inefficient and cannot meet the needs of engineering applications for rapid material screening.

[0003] Several risk assessment models based on the current state of pollutants have been developed in the prior art. For example, prior art CN114862203A discloses a method for assessing the health risks of applying biochar-based fertilizers to soil. This method measures the bioavailable content (including acid-soluble, reducible, and oxidizable forms) of heavy metals and the toxic equivalent concentration of polycyclic aromatic hydrocarbons (PAHs) in the biochar-based fertilizer, substitutes these values ​​into a lifetime incremental carcinogenic risk (ILCR) model, and uses Monte Carlo simulation to handle parameter uncertainties, ultimately calculating the health risk index and safe application rate. This method provides a framework for real-time health risk assessment of combined pollution (heavy metals-PAHs).

[0004] However, this method has significant limitations: First, it is a static risk assessment model, relying entirely on the initial content and form of pollutants in biochar-based fertilizers. It does not consider the dynamic release behavior of heavy metals after application to the soil, which involves environmental aging processes (such as oxidation, dissolution, and complexation) over several years or even decades. Therefore, it cannot predict the long-term risk evolution over time and cannot answer the crucial question of how to "quantify the risk after 10, 20, or 30 years of application." Second, the method aims to assess the combined carcinogenic risk to human health; its model is complex, involving numerous toxicological and exposure parameters, and is not specifically designed to predict the environmental release behavior of heavy metals.

[0005] Therefore, there is an urgent need for an assessment method and tool that can rapidly and quantitatively predict the long-term release behavior of heavy metals, so as to evaluate the long-term environmental safety of biochar in a more scientific and realistic way, and fill the technological gap between existing static risk assessment models and long-term behavior prediction. Summary of the Invention

[0006] The main objective of this invention is to provide a method for simulating the rhizosphere environment to assess the long-term release risk of heavy metals from biochar, aiming to solve the problems of long assessment cycles and inability to quantitatively predict the long-term release risk of heavy metals from biochar in existing technologies.

[0007] To achieve the above objectives, the present invention provides a method for simulating the rhizosphere environment to assess the long-term release risk of heavy metals from biochar, the method comprising the following steps:

[0008] Step 1: Conduct natural soil incubation experiments and standardized accelerated aging experiments with organic acid solutions for a period of T0 on the homologous biochar samples. The organic acid solution is used to simulate the dissolution and complexation of biochar by plant root exudates and microbial metabolites in the soil. Based on the cumulative release ratio W0 of the target heavy metal after the soil incubation experiment, determine the organic acid aging time t required to achieve the same release ratio. eq To establish a quantitative conversion relationship between organic acid aging time and natural soil cultivation time, wherein the target heavy metal includes at least one of Cd, Zn, Ni, Cr, and Cu;

[0009] Step 2: Perform the standardized organic acid solution accelerated aging experiment on the biochar sample to be evaluated to obtain the cumulative release ratio data W of the target heavy metal at different aging times t. t ;

[0010] Step 3: Based on the quantitative conversion relationship established in Step 1, convert the aging time t in Step 2 into an equivalent natural aging time T, and then convert the equivalent natural aging time T and the corresponding cumulative release ratio data W. t A long-term release kinetic prediction model for the target heavy metal was constructed, and the target assessment period was substituted into the long-term release kinetic prediction model to calculate the predicted cumulative release ratio, so as to assess the risk of heavy metal release after long-term application of biochar.

[0011] Optionally, in steps 1-2, the organic acid solution is an aqueous solution of citric acid, malic acid, or glycolic acid, with a concentration of 1-50 mmol / L.

[0012] Optionally, the organic acid solution is a citric acid solution with a concentration of 10 mmol / L, used to simulate the release of Cd, Zn, Ni, and Cr; or a citric acid solution with a concentration of 15 mmol / L, used to simulate the release of Cu.

[0013] Optionally, the standardized accelerated aging test of organic acid solution involves mixing biochar and organic acid solution at a solid-liquid ratio of 1:20-1:100 g / mL under constant temperature conditions of 20-30℃ and then shaking the mixture, with an aging cycle of 5-10 days.

[0014] Optionally, the quantitative conversion relationship is as follows: 7 days of organic acid aging is equivalent to 1 year of natural soil cultivation.

[0015] Optionally, in step 3, the long-term release kinetic prediction model is a Boltzmann model, a Logistic model, or a logarithmic function model, etc.

[0016] Optionally, in step 3, the target evaluation period is 10 years, 20 years, or 30 years.

[0017] Optionally, the biochar sample is obtained by subjecting the biomass raw material to high-temperature heat treatment under limited or anaerobic conditions. The biomass raw material includes one of the following: sludge, crop straw, and livestock manure.

[0018] Optionally, the prepared biochar may be pre-modified.

[0019] Beneficial effects:

[0020] (1) Organic acids were selected as the aging medium to directly simulate the dissolution and complexation of biochar by rhizosphere exudates at room temperature. The quantitative relationship between "organic acid aging time" and natural aging time was established through experimental calibration, thereby achieving a rapid and quantitative risk assessment that is closer to the real process in agricultural soil. A unique quantitative relationship based on "aging time" was also established - a direct quantitative equivalence relationship between "aging time (days)" and "natural aging years" was discovered. Since the simulation process is closer to the main natural pathway of heavy metal release in agricultural soil (rhizosphere dissolution), the prediction model established based on this has higher reliability and smaller bias in predicting long-term risks in agricultural scenarios.

[0021] (2) The evaluation that takes several years to complete can be shortened to a few weeks, and the experimental procedure is standardized, which is conducive to reproducibility and promotion. The principle of this method is applicable to biochar from different sources and various heavy metals. It is particularly suitable for evaluating biochar products intended for use in soil environments with vegetation growth, such as farmland and forest land, and provides direct and scientific technical basis for their safe application. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of an embodiment of a method for assessing the long-term release risk of heavy metals from biochar by simulating the rhizosphere environment according to the present invention.

[0024] Figure 2 The percentage of heavy metals accumulated and released after the organic acid aging of the sludge liquefaction biochar in Example 1;

[0025] Figure 3 The percentage of heavy metals accumulated after organic acid aging in the apatite-modified sludge liquefaction biochar of Example 1;

[0026] Figure 4 The percentage of heavy metals accumulated after organic acid aging in rice straw pyrolysis biochar in Example 2;

[0027] Figure 5 The percentage of heavy metals accumulated after the organic acid aging of the pig manure pyrolysis biochar in Example 3 is shown.

[0028] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] See Figure 1 This invention provides a schematic flowchart of an embodiment of a method for simulating the rhizosphere environment to assess the long-term release risk of heavy metals from biochar. The method includes the following steps:

[0031] Step 1 - Calibration Step: The homologous biochar samples were subjected to a natural soil incubation experiment (T0) and a standardized accelerated aging experiment using an organic acid solution. The organic acid solution was used to simulate the dissolution and complexation of biochar by plant root exudates and microbial metabolites in the soil. Based on the cumulative release ratio W0 of the target heavy metal after the soil incubation experiment, the required organic acid aging time t to achieve the same release ratio was determined. eq To establish a quantitative conversion relationship between organic acid aging time and natural soil cultivation time.

[0032] The natural soil incubation experiment involves taking a sample of homologous biochar, mixing it evenly with clean soil, and incubating it for a period of T0 under simulated field conditions (such as constant temperature and humidity). After incubation, the cumulative release ratio W0 of the target heavy metal in the biochar is measured. This W0 value represents the actual release level of the biochar after T0 aging in natural soil. T0 is preferably 1 year. The target heavy metal includes at least one of Cd, Zn, Ni, Cr, and Cu.

[0033] The accelerated aging simulation experiment involves taking another sample of biochar from the same source, without mixing it with soil, and directly subjecting it to a standardized accelerated aging experiment using an organic acid solution. Specific conditions include: using an organic acid solution of a specific concentration, and shaking the biochar at a certain solid-liquid ratio at room temperature (20-30℃). This treatment is continuous, and the cumulative release ratio of heavy metals is measured periodically on a daily basis. The organic acid solution is an aqueous solution of citric acid, malic acid, or glycolic acid with a concentration of 1-50 mmol / L; preferably, the organic acid solution is a 10 mmol / L citric acid solution used to simulate the release of Cd, Zn, Ni, and Cr; or a 15 mmol / L citric acid solution used to simulate the release of Cu.

[0034] Furthermore, organic acid aging experiments were continuously conducted, and cumulative release ratio curves were plotted in real time. When the curve showed that the release ratio reached or was very close to the baseline value W0 obtained from the soil incubation experiment, the total organic acid aging time t consumed at this point was recorded. eq Therefore, a core quantitative relationship is established: t eq The duration of organic acid aging is approximately equal to the duration of natural soil aging (T0).

[0035] Furthermore, the biochar samples are obtained by subjecting biomass raw materials to high-temperature heat treatment (usually at 300-700℃) under limited or anaerobic conditions. The biomass raw materials include one of the following: sludge, crop straw, and livestock manure.

[0036] This step directly links the "number of days of organic acid aging," which can be rapidly achieved in the laboratory, with the "number of years of natural aging," which is difficult to observe directly. This ensures that subsequent accelerated experimental predictions are "calibrated" based on behavior in real natural environments, rather than purely theoretical speculation, thus guaranteeing the ecological relevance and reliability of the prediction model. The choice of organic acids as the aging medium is based on the fact that plant root exudates and microbial metabolites contain large amounts of these organic acids, which promote the activation and release of heavy metals in biochar through acidification and complexation (chelation). Therefore, using organic acid aging to simulate natural aging is highly consistent with the main biochemical pathways of heavy metal release in agricultural soils. Assuming that the cumulative dissolution / complexation effect of rhizosphere exudates on biochar in natural soil over one year can be reduced in a shorter time (t) under standardized, continuous organic acid immersion conditions in the laboratory. eq The same chemical effect (i.e., the same heavy metal release W0) was achieved within the same timeframe. Ultimately, 7 days of organic acid aging was equivalent to 1 year of natural soil incubation. The validity of this quantitative relationship confirms the chemical similarity of organic acid-heavy metal complexation reactions.

[0037] Step 2 - Experimental Procedure: The biochar sample to be evaluated was subjected to an accelerated aging experiment using a standardized organic acid solution to obtain the cumulative release ratio data W of the target heavy metal at different aging times t. t .

[0038] Specifically, for new biochar samples requiring evaluation (which may be from the same or different source as the calibration samples), a standardized accelerated aging test with organic acid solution, identical to that in step 1, is directly performed. At room temperature, the samples are continuously treated with an organic acid solution of a specified concentration at multiple pre-set time points (t1, t2, t3, ... t). n Sampling was conducted to determine the cumulative release ratio (W) of the target heavy metal. t1 W t2 W t3 ,...W tn This allows us to obtain a complete release kinetic curve.

[0039] This step significantly accelerates the complexation and desorption of heavy metals in a standardized organic acid solution with a concentration potentially slightly higher than that in the natural rhizosphere, thus simulating the cumulative release effect over several years under natural conditions within days or weeks. All experimental conditions (temperature, concentration, oscillation frequency) are strictly uniform, eliminating random fluctuations in the natural environment, resulting in highly repeatable and comparable experimental results, facilitating risk ranking among different biochar samples.

[0040] Step 3 - Prediction Step: Based on the quantitative conversion relationship established in Step 1, the aging time t in Step 2 is converted into an equivalent natural aging time T. Based on the equivalent natural aging time T and the corresponding cumulative release ratio data W... t A long-term release kinetic prediction model for the target heavy metals was constructed, and the target assessment period was substituted into the model to calculate the predicted cumulative release ratio, thereby assessing the heavy metal release risk of biochar after long-term application. The long-term release kinetic prediction model can be a Logistic model, a logarithmic function model, or a growth function model. The target assessment period is 10-30 years.

[0041] Specifically, using the quantitative relationship established in step 1 (7 days ≈ 1 year), the experimental time series (t1, t2, t3...) obtained in step 2 is converted into the corresponding equivalent natural aging time series (T1, T2, T3...). For example, t1=7 days is converted to T1=1 year, t2=14 days is converted to T2=2 years, and so on; using the converted equivalent natural aging time T as the independent variable and the corresponding cumulative release ratio W as the dependent variable, the data points (T1, W...) are... t1 ), (T2, W t2...The data is input into a computer, and an appropriate mathematical model (such as the Boltzmann model, Logistic model, or logarithmic function model) is selected for nonlinear regression fitting to obtain the optimal prediction equation W=f(T). This equation is the prediction model for the long-term release of heavy metals from the biochar.

[0042] When it is necessary to assess the risk of biochar in the Nth year after application (e.g., 10, 20, or 30 years), simply substitute the target year N into the prediction equation f(T) above to directly calculate the predicted cumulative release ratio W. pred By combining the total amount of heavy metals, a quantitative assessment of the long-term environmental risks of this biochar can be made.

[0043] This step can output a specific numerical value to predict the cumulative release of heavy metals from biochar after any target number of years, thereby transforming long-term, uncertain risks into quantifiable and comparable indicators, providing direct and scientific quantitative basis for the safe application, risk classification and management of biochar.

[0044] Furthermore, the standardized accelerated aging experiment with organic acid solution involves mixing biochar and organic acid solution at a solid-liquid ratio of 1:20-1:100 g / mL under constant temperature conditions of 20-30℃ and then shaking the mixture, with each aging cycle lasting 5-10 days.

[0045] This invention establishes quantitative conversion relationships through "calibration," rapidly acquires behavioral data through "experimentation," and finally outputs a quantitative risk assessment through "prediction." These three steps are interconnected, and their effectiveness is rooted in the highly targeted scientific mechanism of "simulating rhizosphere action with organic acids," thereby achieving a rapid, scientific, and quantitative assessment of the long-term environmental risks of biochar in agriculture.

[0046] Furthermore, to better illustrate the method of the present invention, specific embodiments are described below.

[0047] Example 1

[0048] A certain region plans to liquefy municipal sludge from a wastewater treatment plant to produce sludge-derived biochar, which will then be applied to farmland (soil type: sandy loam). Because the sludge raw material is enriched with heavy metals such as Cd, Zn, Ni, Cr, and Cu, to avoid the potential risk of secondary heavy metal pollution after long-term application, it is necessary to assess the risk of endogenous heavy metal release from the biochar after 10 years of application. Traditional soil cultivation methods require 10 years, severely restricting the efficiency of engineering decision-making. This embodiment, based on the method of this invention, shortens the assessment period from several years to several weeks through organic acid aging experiments, accurately simulating and quantifying the heavy metal release risk of sludge-derived biochar within 10 years, providing a basis for the safe application of biochar in farmland.

[0049] Risk assessment of heavy metal release from sludge liquefaction biochar

[0050] (1) Preparation of biochar: Sludge from a sewage treatment plant was taken as raw material, air-dried, passed through a 100-mesh sieve, and heat-treated in a high-pressure reactor at 300°C for 30 minutes with anhydrous ethanol as solvent to prepare sludge liquefaction biochar (S-BC). This biochar was used to evaluate the proportion of heavy metals released after 10 years of application in actual soil environment.

[0051] (2) Organic acid aging: The prepared sludge liquefaction biochar was added to citric acid, malic acid, and glycolic acid solutions with concentrations of 10, 15, and 30 mmol / L, respectively, and placed in sealed vials. The aging conditions were set as follows: the biochar and organic acid solution were mixed at a solid-liquid ratio of 1:50, and aging was carried out in a constant temperature water bath shaker with parameters set at 25℃ and 150 rpm. An aging cycle was 7 days. During the organic acid aging period, the organic acid solution was replaced every 7 days, and the cumulative release ratio of the target heavy metals (Cd, Zn, Ni, Cr, and Cu) was measured within each cycle. This process was repeated for 10 consecutive cycles of aging experiments according to the standard procedure, simulating the natural aging of biochar in the natural environment for 10 years. The cumulative release ratio of each heavy metal after organic acid aging is shown in the figure below. Figure 2 As shown.

[0052] (3) Soil incubation and establishment of equivalence: Through soil incubation experiments, it was determined that the biochar cultured in soil for 1 year (T) base =1), the baseline values ​​for the release of each heavy metal from biochar were determined. The specific steps of the soil incubation experiment were as follows: biochar was mixed with actual soil at an addition ratio of 3 wt%, and 70% field capacity was maintained. After incubation for a baseline period of 1 year, the baseline values ​​for the release ratio of the target heavy metals (Cd, Zn, Ni, Cr, and Cu) were measured. In this case, the soil incubation experiment was conducted for a total of 3 years, thereby verifying the reliability of the present invention. The release data of each heavy metal are shown in Table 1.

[0053] By directly comparing the experimental data of endogenous heavy metal release from biochar after organic acid aging in step (2), it was determined that at the end of the first organic acid aging cycle (i.e., organic acid aging time t=7 days) under 10 mmol / L citric acid aging conditions, the release ratio (W) of Cd, Zn, Ni, and Cr was equal to the baseline value (W) of heavy metal release ratio of biochar after 1 year of soil cultivation. base Under aging conditions of 15 mmol / L citric acid, at the end of the first organic acid aging cycle (i.e., organic acid aging time t=7 days), the release ratio of Cu (W) was measured to be equal to the baseline value of heavy metal release ratio of biochar after one year of soil incubation (W). baseTherefore, the core equivalence relationship was directly determined through experimental data: 7 days of organic acid aging is equivalent to 1 year of field soil cultivation.

[0054]

[0055] Model fitting: Based on the organic acid aging experimental data obtained in step (2), nonlinear fitting was performed, and the parameters and equations obtained are as follows:

[0056] Cd: W = -134.99 / (1+e (T-4.09) / 2.66 )+113.35; R²=0.99

[0057] Zn: W = -117.38 / (1+e (T-4.61) / 2.27 )+107.96; R²=0.99

[0058] Ni: W = -55.45 / (1+e (T-0.61) / 2.86 )+30.62; R²=0.99

[0059] Cr: W=6.06ln(T-0.83)+20.07; R²=0.99

[0060] Cu: W = -36.31 / (1+e (T-8.26) / 1.28 )+37.73; R²=0.99

[0061] (5) Simulation results: Substituting T=10 (year) into the equation model corresponding to different heavy metals in biochar, the results are shown in Table 2:

[0062]

[0063] Table 2 shows that, when organic acid aging was used to simulate the release of endogenous heavy metals from liquefied biochar in farmland for 10 years, the cumulative release rates of endogenous Cd, Zn, Ni, Cr, and Cu were 100%, 97.96%, 28.62%, 33.50%, and 30.31%, respectively. Decision-makers can assess the acceptability of this release level by considering soil environmental quality standards, background values, and ecological risk thresholds.

[0064] Risk assessment of apatite-modified sludge liquefaction biochar

[0065] To address the high risk of heavy metal release from sludge liquefaction biochar (S-BC), apatite was selected for modification to improve the stability of heavy metal compounds, and the modification effect was verified using the method of this invention.

[0066] (1) Preparation of modified biochar: Apatite was selected for biochar modification. 10 wt% of apatite was added to the sludge raw material, and after thorough mixing, it was liquefied according to the preparation method of S-BC to obtain apatite modified sludge liquefied biochar (SA-BC).

[0067] (2) Organic acid aging: The organic acid aging process is consistent with that of S-BC. A aging experiment was conducted for 10 consecutive cycles according to the standard process, simulating 10 years of natural aging of biochar in the natural environment. The cumulative release ratio of various heavy metals after organic acid aging is as follows: Figure 3 As shown.

[0068] (3) Model fitting: Based on the experimental data results in step (2), nonlinear fitting was performed. The parameters and equations for the simulated release of various endogenous heavy metals from apatite-modified sludge biochar are as follows:

[0069] Cd: W = -93.83 / (1+e (T-4.66) / 2.48 )+84.15; R²=0.99;

[0070] Zn: W = -85.69 / (1+e (T-4.61) / 2.27 )+78.81; R²=0.99;

[0071] Ni: W = -36.94 / (1+e (T-2.86) / 1.69 )+36.99; R²=0.99;

[0072] Cr: W=3.88ln(T-0.78)+11.52; R²=0.99;

[0073] Cu: W = -28.32 / (1+e (T-8.24) / 1.26) +29.55; R²=0.99;

[0074] (4) Simulation results: Substituting T=10 (year) into the equation model corresponding to different heavy metals in biochar, the results are shown in Table 3:

[0075]

[0076] Compared to S-BC, after modification with apatite, the release rates of Cd and Zn in SA-BC decreased to 74.39% and 71.51%, respectively, while the release rates of Cr and Cu also decreased to 20.14% and 23.93%, respectively. Decision-makers can assess whether this release level is acceptable by considering soil environmental quality standards, background values, and ecological risk thresholds.

[0077] Example 2

[0078] A local government plans to prepare rice straw pyrolysis biochar from rice straw contaminated with heavy metals through pyrolysis and apply it to farmland (soil type: sandy loam). Because the contaminated rice straw is enriched with heavy metals such as Cd, Zn, Ni, Cr, and Cu, to avoid the potential risk of secondary heavy metal pollution after long-term application, it is necessary to assess the risk of endogenous heavy metal release from the biochar after 20 years of application. Traditional soil cultivation methods take 20 years, which cannot meet the need for rapid decision-making in the early stages of the project. This embodiment utilizes the method of the present invention to accurately simulate and quantify the release risk of Cd, Zn, Ni, Cr, and Cu from rice straw pyrolysis biochar over 20 years, providing a basis for the safe application of biochar in farmland.

[0079] (1) Preparation of biochar: Rice straw from a farmland contaminated with heavy metals was used as raw material. It was air-dried and passed through a 100-mesh sieve. The raw material was placed in an industrial pyrolysis furnace and pyrolyzed at 500℃ for 30 min to obtain rice straw pyrolysis biochar (R-BC). This biochar was used to evaluate the proportion of heavy metals released after 20 years of application in a real soil environment.

[0080] (2) Organic acid aging: Biochar was aged in a 10 mmol / L citric acid solution. The aging conditions were set as follows: biochar and organic acid solution were mixed at a solid-liquid ratio of 1:50, and aging was carried out in a constant temperature water bath shaker at 25℃ and 150 rpm. An aging cycle was 7 days. During the organic acid aging period, the organic acid solution was replaced every 7 days, and the cumulative release ratios of Cd, Zn, Ni, and Cr were measured within each cycle. Alternatively, biochar was aged in a 15 mmol / L citric acid solution, with the other steps the same as before, and the release of Cu was measured. This process was repeated for 20 consecutive cycles of aging experiments according to the standard procedure, simulating 20 years of natural aging of biochar in the natural environment. The cumulative release ratios of each heavy metal after organic acid aging are shown in the figure below. Figure 4 As shown.

[0081] (3) Model fitting: Based on the experimental data results in step (2), nonlinear fitting was performed, and the parameters and equations for the simulated release of various endogenous heavy metals from rice straw pyrolysis biochar (R-BC) are as follows:

[0082] Cd: W = -105.65 / (1+e (T-6.70) / 3.09 )+103.73; R²=0.99;

[0083] Zn: W = -109.61 / (1+e (T-6.86) / 3.27 )+103.48; R²=0.99;

[0084] Ni: W=13.76ln(T+1.50)-9.66; R²=0.99;

[0085] Cr: W=15.43ln(T+0.33)+2.35; R²=0.99;

[0086] Cu: W = -59.58 / (1+e (T-10.11) / 3.85 )+56.79; R²=0.99;

[0087] (4) Simulation results: Substituting T=20 (year) into the equation model corresponding to different heavy metals in biochar, the results are shown in Table 4:

[0088]

[0089] Table 4 shows that, when organic acid aging was used to simulate the release of endogenous heavy metals from rice straw pyrolysis biochar applied in farmland for 20 years, the cumulative release rates of endogenous Cd, Zn, Ni, Cr, and Cu were 100%, 100%, 32.56%, 48.83%, and 52.55%, respectively. Decision-makers can assess the acceptability of this release level by considering soil environmental quality standards, background values, and ecological risk thresholds.

[0090] Example 3

[0091] A local government plans to use pyrolysis of pig manure from a pig farm to produce pig manure biochar for application in farmland (soil type: sandy loam). Because pig manure is rich in heavy metals such as Cd, Zn, Ni, Cr, and Cu, to avoid the potential risk of secondary heavy metal pollution after long-term application, it is necessary to assess the risk of endogenous heavy metal release from the biochar after 30 years of application. Traditional soil cultivation methods take 30 years, which cannot meet the need for rapid decision-making in the early stages of the project. This embodiment utilizes the method of the present invention to accurately simulate and quantify the release risk of Cd, Zn, Ni, Cr, and Cu from pig manure pyrolysis biochar over 30 years, providing a basis for the safe application of biochar in farmland.

[0092] (1) Preparation of biochar: Pig manure from a pig farm was used as raw material, air-dried, and passed through a 100-mesh sieve. The raw material was placed in an industrial pyrolysis furnace and continuously pyrolyzed at 500℃ for 30 min to obtain pig manure pyrolysis biochar (M-BC). This biochar was used to evaluate and predict the proportion of heavy metals released after 30 years of application in a real soil environment.

[0093] (2) Organic acid aging: The organic acid aging process is the same as step (2) in Example 2. An aging experiment was conducted for 30 consecutive cycles according to the standard procedure to simulate the natural aging of biochar in a natural environment for 30 years. The cumulative release ratio of each heavy metal after organic acid aging is as follows: Figure 5 As shown.

[0094] (3) Model fitting: Based on the experimental data results in step (2), nonlinear fitting was performed. The parameters and equations for the simulated release of various endogenous heavy metals from pig manure pyrolysis biochar (M-BC) are as follows:

[0095] Cd: W = -124.56 / (1+e (T-5.88) / 4.53 +98.71; R²=0.99

[0096] Zn: W = -153.08 / (1+e (T-4.37) / 6.47 +100.81; R²=0.99

[0097] Ni: W=12.17ln(T-0.12)+6.99; R²=0.99

[0098] Cr: W=11.53ln(T+0.45)-2.11; R²=0.99

[0099] Cu: W = -62.23 / (1+e (T-10.03) / 5.47 )+53.39; R²=0.99

[0100] (4) Simulation results: Substituting T=30 (year) into the equation model corresponding to different heavy metals in biochar, the results are shown in Table 5:

[0101]

[0102] According to the method of the present invention, organic acid aging was used to simulate the release of endogenous heavy metals after 30 years of application of pig manure pyrolysis biochar in farmland. The cumulative release rates of endogenous Cd, Zn, Ni, Cr, and Cu were 100%, 100%, 32.56%, 48.83%, and 52.55%, respectively. Decision-makers can determine whether this release level is acceptable by combining soil environmental quality standards, background values, and ecological risk thresholds.

[0103] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for simulating the rhizosphere environment to assess the long-term release risk of heavy metals from biochar, characterized in that, The method includes the following steps: Step 1: Conduct natural soil incubation experiments and standardized accelerated aging experiments with organic acid solutions for a period of T0 on the homologous biochar samples. The organic acid solution is used to simulate the dissolution and complexation of biochar by plant root exudates and microbial metabolites in the soil. Based on the cumulative release ratio W0 of the target heavy metal after the soil incubation experiment, determine the organic acid aging time t required to achieve the same release ratio. eq To establish a quantitative conversion relationship between organic acid aging time and natural soil cultivation time, wherein the target heavy metal includes at least one of Cd, Zn, Ni, Cr, and Cu; Step 2: Perform the standardized organic acid solution accelerated aging experiment on the biochar sample to be evaluated to obtain the cumulative release ratio data W of the target heavy metal at different aging times t. t ; Step 3: Based on the quantitative conversion relationship established in Step 1, convert the aging time t in Step 2 into an equivalent natural aging time T, and then convert the equivalent natural aging time T and the corresponding cumulative release ratio data W. t A long-term release kinetic prediction model for the target heavy metal was constructed, and the target assessment period was substituted into the long-term release kinetic prediction model to calculate the predicted cumulative release ratio, so as to assess the risk of heavy metal release after long-term application of biochar.

2. The method as described in claim 1, characterized in that, In steps 1-2, the organic acid solution is an aqueous solution of citric acid, malic acid, or glycolic acid with a concentration of 1-50 mmol / L.

3. The method as described in claim 2, characterized in that, The organic acid solution is a 10 mmol / L citric acid solution used to simulate the release of Cd, Zn, Ni, and Cr; or a 15 mmol / L citric acid solution used to simulate the release of Cu.

4. The method as described in claim 1, characterized in that, The standardized accelerated aging test of organic acid solution involves mixing biochar and organic acid solution at a solid-liquid ratio of 1:20-1:100 g / mL under constant temperature conditions of 20-30℃ and then shaking the mixture, with each aging cycle lasting 5-10 days.

5. The method as described in claim 4, characterized in that, The quantitative conversion relationship is as follows: 7 days of organic acid aging is equivalent to 1 year of natural soil cultivation.

6. The method as described in claim 1, characterized in that, In step 3, the long-term release kinetic prediction model is a Boltzmann model, a Logistic model, or a logarithmic function model.

7. The method as described in claim 1, characterized in that, In step 3, the target evaluation period is 10 years, 20 years, or 30 years.

8. The method according to any one of claims 1 to 7, characterized in that, Biochar samples are obtained by high-temperature pyrolysis of biomass raw materials under limited or anaerobic conditions. The biomass raw materials include one of the following: sludge, crop straw, and livestock manure.

9. The method as described in claim 8, characterized in that, The prepared biochar was pre-modified.

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