Modified bacteria stick biochar, preparation method thereof and application of modified bacteria stick biochar in soil remediation

Abstract

The invention provides modified mushroom stick biochar, a preparation method thereof and application of the modified mushroom stick biochar in soil remediation, and the preparation method specifically comprises the following steps: carbonizing lignin-removed mushroom stick residues to obtain biochar; mixing the biochar with a calcium chloride solution, filtering, drying, grinding and sieving to obtain calcium modified biochar; the calcium modified biochar and humic acid are mixed and then placed in deionized water, the mixture is stirred to react and then filtered, filter residues are air-dried, modified bacteria stick biochar is obtained, and the mass ratio of the calcium modified biochar to the humic acid is (5-19): 1. The modified bacteria stick biochar prepared by the preparation method can increase the specific surface area and pore structure of the biochar, increase the hydrophilicity and surface polar functional groups of the biochar, and reduce the soil hardening degree, the available lead content and the available cadmium content.

Description

Technical Field

[0001] The present invention relates to the field of modified biochar, and specifically, to a modified mushroom stick biochar, a preparation method thereof, and an application thereof in soil remediation. Background Art

[0002] As a new type of carbon-rich material, biochar has strong adsorption and regulation capabilities, high pH characteristics, abundant functional groups, and a large number of ion exchange sites. It can promote nutrient cycling and carbon sequestration in the soil, change the abundance and activity of microorganisms, reduce the toxicity, acidity, and alkalinity of heavy metals in the soil, and promote crop growth. However, there are also certain differences in the performance of biochar materials prepared from different raw materials by carbonization. The morphology, surface functional groups, and microstructure of biochar prepared by conventional methods cannot fully meet the properties required by problem soils, and the unreasonable application of biochar can have an adverse impact on the soil. For example, the soluble alkali ions and mineral ions in biochar can increase the content of some nutrient cations in the soil, but the carbonates and oxygen-containing functional groups in it can also increase the soil alkalinity, causing an increase in the soil conductivity, pH value, and the concentration of certain salt ions, thereby resulting in soil property degradation, decreased permeability, and unbalanced nutrient adsorption and exchange. Therefore, excessive application of biochar base fertilizer can increase the risk of salinization of farmland soil.

[0003] The application publication number CN109174001A discloses a method for preparing calcium-modified litchi biochar and using it to reduce estrone in water, belonging to the field of ecological environment remediation. The calcium-modified litchi biochar is prepared by the following method: after washing litchi wood strips, drying them to a constant weight, crushing them and sieving them through a 60-mesh sieve to obtain a powdery material, mixing it with a calcium chloride solution with a concentration of 40 g / L, performing ultrasonic reaction at a temperature of 40 °C for 2 h, then oscillating at room temperature for 2 h, performing rapid pyrolysis at a temperature of 650 °C and under a nitrogen atmosphere for 2 h, cooling and grinding, and sieving through a 60-mesh sieve to obtain calcium-modified litchi biochar. The prepared calcium-modified biochar can effectively remove estrone in water and significantly reduce the point source pollution caused by intensive livestock and poultry farming. Moreover, the method for preparing the calcium-modified litchi biochar can significantly reduce the usage amount of calcium chloride and effectively reduce the risk of secondary pollution. However, the method for preparing the calcium-modified litchi biochar only discloses that litchi can be used to make biochar and perform calcium modification, and then be applied to remove estrone in water, and does not disclose that it can be applied to the soil to improve the soil nutrient components, reduce soil compaction, and adsorb heavy metals in the soil. Summary of the Invention

[0004] In order to increase the specific surface area and pore structure of biochar, increase the hydrophilicity and surface polar functional groups of biochar, reduce the degree of soil compaction, and the contents of available lead and available cadmium by selecting appropriate biochar sources and modification means, the technical solution adopted by the present invention is: a preparation method of a modified mushroom stick biochar, comprising the following steps:

[0005] Preparation of biochar: The lignin-removed Lentinula edodes stick residue is carbonized to obtain biochar;

[0006] Preparation of calcium-modified biochar: The biochar is mixed with calcium chloride solution, filtered, and then dried, ground, and sieved to obtain calcium-modified biochar;

[0007] Preparation of modified stick biochar: The calcium-modified biochar and humic acid are mixed and placed in deionized water. After stirring and reacting, filtration is carried out. The filter residue is air-dried to obtain modified stick biochar, that is, calcium-modified biochar modified by humic acid. Among them, the mass ratio of the calcium-modified biochar to the humic acid is (5-19):1. Among them, the specific surface area of the modified stick biochar is 74.63 m 2 / g - 92.62 m 2 / g, and the pore volume is 0.119 cm 3 / g - 0.171 cm 3 / g.

[0008] Based on the above, the specific steps of the preparation of biochar include:

[0009] The Lentinula edodes stick residue is washed with deionized water, dried, crushed, and sieved. The obtained Lentinula edodes stick residue powder is stirred in NaOH solution for 3 h - 8 h to remove the lignin in the components of the Lentinula edodes stick residue powder. After filtration, grinding, and sieving, carbonization treatment is carried out for 1 h - 3 h under the conditions of N2 atmosphere, carbonization temperature of 400 °C - 800 °C, and heating rate of 3 °C / min - 10 °C / min to obtain the biochar. Among them, the specific surface area of the biochar is 40.63 m 2 / g, and the pore volume is 0.053 cm 3 / g.

[0010] Based on the above, the specific steps of the preparation of calcium-modified biochar include:

[0011] According to the standard of adding 2 g - 10 g of the biochar to every 50 mL of calcium chloride solution, the biochar is added to the calcium chloride solution, stirred at room temperature for 12 h - 24 h, and then the reaction solution is suction-filtered. The obtained filter residue is washed with deionized water and then dried at a temperature of 80 °C - 120 °C. The obtained black solid is ground and sieved to obtain the calcium-modified biochar.

[0012] The present invention also provides an application of the modified stick biochar as a soil repair agent in soil repair.

[0013] Based on the above, when the modified stick biochar can be used as a soil repair agent for soil repair, the mass ratio of the modified stick biochar to the soil is 1:(5 - 15).

[0014] The present invention has outstanding substantive features and significant progress compared with the prior art. Specifically, a modified mushroom stick biochar, its preparation method and application in soil remediation provided by the present invention are disclosed. By using humic acid and calcium ions in combination to modify the mushroom stick biochar, compared with the raw materials of unmodified biochar, the modified mushroom stick biochar exhibits a higher specific surface area, pore volume, ash content, and a lower yield. Moreover, it can also show the characteristics of less ash, high yield, large specific surface area, and high pore volume. At the same time, grafting humic acid onto the surface of calcium-modified biochar can significantly increase the content of oxygen-containing groups, benzene rings, and carbon chains, thereby providing necessary organic matter for the soil and offering the potential possibility to inhibit the migration of heavy metal ions in the soil. Additionally, humic acid modification and calcium modification change the surface structure of the biochar, increase the specific surface area of the particles, and enrich the pore structure. Meanwhile, the modification treatment reduces the degree of aromatization of the biochar, increases the hydrophilicity and surface polar functional groups of the biochar, so that it can be used as a soil remediation agent to repair the soil.

[0015] Furthermore, experiments show that when using the modified mushroom stick biochar prepared from Lentinula edodes mushroom stick residue to repair the soil, the pH value, conductivity, and organic matter content of the soil all increase. And after the repair, the activities of urease, sucrase, and alkaline phosphatase in the soil all increase, while the activity of peroxidase decreases. At the same time, the enzyme activity in the sample soil will increase with the increase of soil incubation time. When the soil incubation time exceeds 45 days, the improvement effect of soil fertility is the most significant.

[0016] Meanwhile, in the sample soil improved by the soil remediation agent, the contents of available lead and available cadmium both decrease, and the time period during which the contents of available lead and available cadmium decrease significantly is the initial stage of soil incubation (within 0 - 60 days). And after the repair, the contents of fixed Pb and fixed Cd in the soil increase, while the contents of acid-soluble exchangeable Pb and acid-soluble exchangeable Cd decrease. Description of the Drawings

[0017] Figure 1 SEM photos of biochars and their matrices prepared from different biomass raw materials. Among them, Figure 1 A, D, and G respectively refer to the biochar prepared from mushroom stick residue, calcium-modified biochar, and humic acid-modified calcium-modified biochar; B, E, and H respectively refer to the biochar prepared from peanut shells, calcium-modified biochar, and humic acid-modified calcium-modified biochar; C, F, and I respectively refer to the biochar prepared from wood chips, calcium-modified biochar, and humic acid-modified calcium-modified biochar; J - L respectively refer to three kinds of humic acid-modified calcium-modified biochars prepared by ball milling method.

[0018] Figure 2 SEM photos of calcium-modified biochars modified with different concentrations of humic acid. Among them,Figure 2 In this, A refers to the spent mushroom substrate biochar; B - D are humic acid - modified calcium - modified biochars, where the mass ratios of biochar to humic acid are 15:1, 10:1, and 5:1 respectively.

[0019] Figure 3 It is the infrared spectrogram of the humic acid - modified calcium - modified biochar and its parent.

[0020] Figure 4 It is the infrared spectrogram of the calcium - modified biochars modified with different concentrations of humic acid.

[0021] Figure 5 It is the change diagram of soil pH at different remediation times.

[0022] Figure 6 It is the change diagram of soil electrical conductivity at different remediation times.

[0023] Figure 7 It is the change diagram of soil organic matter content at different remediation times.

[0024] Figure 8 It is the change diagram of soil urease activity at different remediation times.

[0025] Figure 9 The change diagram of soil sucrase activity at different remediation times.

[0026] Figure 10 The change diagram of soil alkaline phosphatase activity at different remediation times.

[0027] Figure 11 It is the change diagram of soil catalase activity at different remediation times.

[0028] Among them, Figures 5 to 11 in this, A, B, C, and D respectively refer to the soil pH values at the 15th d, 30th d, 45th d, and 60th d of remediation; 1 - 1, 1 - 3, and 1 - 5 respectively represent adding the soil remediation agent QCa@PSC - 600@HA - 1 to the soil sample at ratios of 1%, 3%, and 5%; 2 - 1, 2 - 3, and 2 - 5 respectively represent adding the soil remediation agent QCa@PSC - 600@HA - 2 to the soil sample at ratios of 1%, 3%, and 5%; 3 - 1, 3 - 3, and 3 - 5 respectively represent adding the soil remediation agent QCa@PSC - 600@HA - 3 to the soil sample at ratios of 1%, 3%, and 5%; 4 - 1, 4 - 3, and 4 - 5 respectively represent adding the soil remediation agent QCa@MDC - 600@HA - 2 to the soil sample at ratios of 1%, 3%, and 5%; the control represents that no soil remediation agent is added to the soil sample.

[0029] Figure 12 It is the morphological distribution diagram of Pb and Cd elements in the improved soil sample No. 1 at different time periods.

[0030] Figure 13 It is the morphological distribution diagram of Pb and Cd elements in the improved soil sample No. 2 at different time periods.

[0031] Among them, Figure 12 and Figure 13 in 1-1, 2-1, 3-1 and 4-1 respectively refer to adding the remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 to the corresponding soil of sample No. 1 or No. 2 at a dose of 1% respectively, and 1-3, 2-3, 3-3 and 4-3 respectively refer to adding the remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 to the corresponding soil of sample No. 1 or No. 2 at a dose of 3%, and 1-5, 2-5, 3-5 and 4-5 respectively refer to adding the soil remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 to the corresponding soil of sample No. 1 or No. 2 at a dose of 5%.

[0032] Figure 14 It is the comparison diagram of the growth of pakchoi. Among them, from left to right in the first row are the control and the soils added with different types of biochar-based composites; the second row is the pakchoi potted plants planted in the flowerpots corresponding to the first row; the third row is the pakchoi plants (36d) in the flowerpots corresponding to the first row; the fourth row is the pakchoi (30d) planted in large quantities in the simulated field-collected soil in the greenhouse.

[0033] Figure 15 It is the diagram of the influence of biochar-based composites on the chlorophyll content in pakchoi.

[0034] Figure 16 It is the diagram of the influence of biochar-based composites on the soluble protein content in pakchoi.

[0035] Figure 17 It is the diagram of the influence of biochar-based composites on the soluble sugar content in pakchoi.

[0036] Among them, Figures 15 to 17Samples 1-1, 1-2, and 1-3 respectively refer to soil samples added with soil remediation agent QCa@PSC-600@HA-1 at ratios of 1%, 3%, and 5%; 2-1, 2-2, and 2-3 respectively refer to soil samples added with soil remediation agent QCa@PSC-600@HA-2 at ratios of 1%, 3%, and 5%; 2-1, 2-2, and 2-3 respectively refer to soil samples added with soil remediation agent QCa@PSC-600@HA-3 at ratios of 1%, 3%, and 5%; Control - soil without soil remediation agent.

[0037] Figure 18 It is the morphological distribution map of Pb and Cd in the soil before and after harvesting Chinese cabbage. Specific implementation manner

[0038] The technical solution of the present invention will be further described in detail through specific implementation manners below.

[0039] Embodiment

[0040] This embodiment provides a preparation method of modified mushroom stick biochar, including the following steps:

[0041] Preparation of biochar powder: First, wash and dry the mushroom stick residue with deionized water, then crush and screen it with a pulverizer (through a 60-mesh steel sieve). The obtained mushroom stick residue powder is stirred in hot alkali solution (5% NaOH solution) for 6 h to remove part of the lignin in its components. Finally, wash the filter residue with deionized water until neutral, dry, grind, and sieve to obtain the biomass pretreatment sample. The mushroom stick residue used in the experiment is the waste mushroom stick residue (MD) from a mushroom planting base in Biyang County, Zhumadian.

[0042] Place the pretreated mushroom stick residue powder in a tubular heating rate furnace under N2 atmosphere for carbonization treatment. The carbonization temperatures are set at 400 °C, 600 °C, and 800 °C respectively, and the heating rate and carbonization time are 5 °C / min and 2 h respectively. After the reaction ends, the obtained black solid is the biochar product. According to the yields and infrared spectra of the biochars obtained from the same biomass raw material at different carbonization temperatures, biochar products with higher carbonization yields and rich surface groups are selected, and their naming numbers are MDC-600, PSC-600, and SDC-600 respectively.

[0043] Preparation of calcium-modified biochar powder: Method 1: Using calcium chloride as the calcium source. Weigh 5 g of biochar powder and transfer it to 250 mL of 1 mol / L calcium chloride solution. Stir the solution at room temperature for 24 h. After the reaction is completed, filter the reaction solution by suction. Wash the obtained filter residue with deionized water and then place it in an oven at 105 °C for drying. The obtained black solid is ground and sieved to obtain calcium-modified biochar powder, and its name and number are respectively: HCa@PSC-600, HCa@MDC-600, and HCa@SDC-600. Method 2: Carbonize eggshells at 600 °C for 2 h, and set the heating rate to 5 °C / min. Before carbonizing the eggshells, it is necessary to perform operations such as cleaning, air drying, crushing, and sieving (100 mesh) in advance. Then, mix the eggshell powder and biochar powder in a mass ratio of 5:1, and perform ball milling under the action of ethanol solvent. The temperature and rotation speed of ball milling are respectively set at 70 °C and 30 r / min. After 4 h, separate the solid, and place the dried solid powder in a tubular heating furnace at 800 °C under N2 atmosphere for burning, and adjust the heating rate of the furnace to 20 °C / min. After 1.5 h, the obtained calcium-modified biochar samples, and their name and number are respectively: QCa@PSC-600, QCa@MDC-600, and QCa@SDC-600.

[0044] Preparation of calcium-humic acid modified biochar composite: Mix calcium-modified biochar powder and humic acid according to the set ratio, transfer it to 50 mL of deionized water, and stir the reaction solution at room temperature. Filter the reaction solution after 8 h, and the obtained filter residue is naturally air-dried to obtain modified mushroom stick biochar.

[0045] For the convenience of comparison, in this example, peanut shells (PS) locally grown and with kernels removed and sawdust (SD) from the woodworking workshop in the innovation and entrepreneurship park on the campus of Huanghuai University are also used to replace mushroom stick residues for the preparation of biochar powder.

[0046] Among them, the mixing ratios of calcium-modified biochar and humic acid were respectively set as: 15:1 (w / w), 10:1 (w / w), and 5:1 (w / w), and the corresponding product numbers were: HCa@PSC-600@HA-1, HCa@MDC-600@HA-1, HCa@SDC-600@HA-1, QCa@PSC-600@HA-1, QCa@MDC-600@HA-1, QCa@SDC-600@HA-1, HCa@PSC-600@HA-2, HCa@MDC-600@HA-2, HCa@SDC-600@HA-2, QCa@PSC-600@HA-2, QCa@MDC-600@HA-2, QCa@SDC-600@HA-2, HCa@PSC-600@HA-3, HCa@MDC-600@HA-3, HCa@SDC-600@HA-3, QCa@PSC-600@HA-3, QCa@MDC-600@HA-3, and QCa@SDC-600@HA-3. That is, humic acid-modified calcium-modified biochar. The experiment tested the physicochemical properties of a series of humic acid-modified calcium-modified biochars obtained by modifying with different calcium sources and modifying with different concentrations of humic acid. The relevant results are shown in Table 1. Among them, HCa refers to using calcium chloride as the calcium source; QCa refers to using eggshells as the calcium source.

[0047] It can be seen from Table 1 that before the carbonization of the three agricultural wastes, they need to be pretreated with alkali in advance, and the obtained biochars are all alkaline. Compared with the modified biochars, the three unmodified biochars all show lower ash content and pore volume, and higher yield and specific surface area. For the three unmodified biochars, the biochar prepared from the spent mushroom substrate shows the characteristics of less ash, high yield, large specific surface area, and low pore volume. During the preparation of the modified biochars, as the dosage of humic acid increases, the pH value of the prepared carbon-based composites decreases more significantly.

[0048] The reason for this phenomenon is that the humic acid solution shows a certain acidity. In addition, there is about 8% ash content in the newly prepared humic acid-modified calcium-modified biochar, and as the usage amount of humic acid increases, the ash content in the biochar composite gradually decreases.

[0049] By comparing the specific surface area and pore volume of the humic acid-modified calcium-modified biochars with different concentrations of humic acid, it is found that for the biochars prepared from the same kind of biomass carbonization, when the mass ratio of humic acid to calcium-modified biochar is 1:10, the specific surface area and pore volume of the prepared humic acid-modified calcium-modified biochar are both large. Different types of biochar raw materials are modified with the same concentration of humic acid solution, and the specific surface area and porosity of the obtained humic acid-modified calcium-modified biochars are also different. However, the influence of the difference in biochar raw material types on the specific surface area and pore volume of the modified biochars is relatively small.

[0050] Table 1 Basic physical and chemical properties of humic acid-modified calcium-modified biochar with different raw materials

[0051]

[0052] Structure characterization

[0053] The apparent morphological characteristics of humic acid-modified calcium-modified biochar and its parent prepared from mushroom stick residue, peanut shell and sawdust as raw materials are shown in Figure 1 as follows. From Figure 1 it can be seen that for the mushroom stick residue biochar, its surface is a hollow tubular fiber structure and the tube wall is relatively smooth. After the modification treatment, the mushroom stick residue-based biochar shows a fragmented structure with a smaller particle size. Obvious holes appear on the surface of some of its particles, and some small pores also appear, indicating that the humic acid modification and calcium modification treatments have changed the surface morphological structure of the mushroom stick biochar. At the same time, there are some irregular ellipsoidal substances on the surface of the modified biochar, indicating that part of calcium (calcium chloride or carbonized eggshell) elements are doped on the biochar surface.

[0054] For the peanut shell-based biochar, after carbonization, the surface of the biochar still retains the original fiber structure of the biomass, with micropores of different sizes distributed on its surface and many surface wrinkles. Compared with the unmodified biochar, in addition to being covered with more pores and wrinkles, the surface of the modified biochar also shows more fine particles, its structure is more fluffy, and the layered structure is more obvious. For the sawdust-based biochar, after the sawdust is carbonized, the surface of the sawdust biochar shows a rough surface morphology and there are many impurities attached, and the pores are relatively few. After the modification treatment, the impurity residues and ash on the surface of the sawdust biochar are removed and it becomes smooth. At the same time, after the modification treatment, the pore structure on the surface of the sawdust-based biochar increases and its structure is more fluffy.

[0055] The apparent morphological characteristics of humic acid-modified calcium-modified biochar prepared by humic acid modification with different concentrations are shown in Figure 2 as follows. From Figure 2It can be seen that as the concentration of the humic acid modifier increases, the number of fine pores on the surface of the modified biochar increases, indicating that humic acid can destroy the microstructure of the biochar surface. However, as the dosage of humic acid further increases, some pores on the biochar surface are blocked. In summary, when using humic acid to modify calcium-modified biochar, in order to ensure the high specific surface area and well-developed pore structure of the modified biochar, biochar-based composites with relatively strong remediation ability for problem soils are screened out, which are QCa@PSC-600@HA-1, HCa@PSC-600@HA-2, HCa@MDC-600@HA-2, QCa@PSC-600@HA-2, QCa@MDC-600@HA-2, HCa@PSC-600@HA-3 and QCa@PSC-600@HA-3 respectively.

[0056] Infrared spectroscopy analysis

[0057] The infrared spectra of the calcium humic acid modified biochar composite material and its matrix prepared from waste mushroom stick residue are shown in Figure 3 as follows. As can be seen from Figure 3 it, for the infrared spectrum of the unmodified mushroom stick residue biochar, the strong and broad vibration absorption peak at the wavenumber of 3422 cm -1 belongs to the stretching vibration of hydroxyl groups, and the vibration absorption peak at the wavenumber of 2834 cm -1 is caused by the C-H stretching vibration on -CH2, the absorption peak at the wavenumber of 1365 cm -1 is caused by the skeletal bending vibration on the benzene ring, the absorption peak at the wavenumber of 1628 cm -1 is caused by the C=O stretching vibration, and the characteristic absorption peak at the wavenumber of 1147 cm -1 is caused by the C-O stretching vibration. Compared with the unmodified mushroom stick residue biochar, the overall functional group composition of the mushroom stick biochar after being modified with calcium chloride and humic acid changes little. However, the intensities of the absorption peaks of the mushroom stick biochar after being modified with calcium chloride and humic acid are all enhanced. At the same time, the positions and intensities of the vibration absorptions on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 are almost the same, indicating that the differences in the functional group composition and content on the surfaces of these two modified biochars are not obvious.

[0058] In addition, on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2, there are respectively at 775 cm -1 and 776 cm -1New absorption peaks appear at the wavenumbers. This is attributed to the action of C-Ca bonds on the surface of the modified biochar. Meanwhile, humic acid is modified on the surface of the biochar, and a large number of oxygen-containing functional groups are introduced onto the biochar surface during this process, resulting in enhanced vibration absorptions at the wavenumbers of 3422 cm -1 and 1628 cm -1 for the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2, indicating an increase in the content of acidic groups on the surface of the humic acid-modified calcium-modified biochar.

[0059] The infrared spectra of the calcium-modified biochar modified with different concentrations of humic acid are shown in Figure 4 as follows. As can be seen from Figure 4 , changing the concentration of humic acid has little effect on the chemical composition of the humic acid-modified calcium-modified biochar, indicating that the changes in the content and composition of the oxygen-containing polar groups and organic matter on the surface of the humic acid-modified calcium-modified biochar prepared by using different concentrations of humic acid modifiers are not reflected in the infrared spectra. However, precisely due to the abundant polar groups on the surface of the modified biochar, when it is applied to farmland with problems of soil compaction and heavy metal pollution, it can improve the air permeability and water retention capacity of the soil by changing the soil aggregate structure, and can also adsorb heavy metal ions in the soil through ion exchange, surface complexation, etc. At the same time, there is no difference in the morphological characteristics between the modified biochar prepared by the ball milling method and the modified biochar prepared by the chemical impregnation method. In view of the fact that the preparation of calcium-modified biochar by the ball milling method can reduce the types and amounts of chemical reagents, subsequent experiments will be carried out using QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 as raw materials.

[0060] Elemental analysis

[0061] The percentage contents of C, H, N and S elements in the biochar samples are determined using an elemental analyzer, and the content of O element can be calculated by the subtraction method. The organic elemental compositions and contents of the calcium humic acid-modified biochar composites and their precursors are shown in Table 2. Specifically, the H / C molar ratio of the biochar material can be used as an index to measure its degree of aromatization, while the O / C molar ratio is positively correlated with the oxygen-containing functional groups on its surface, and it can also be used as a basis for judging the hydrophilicity of the biochar material. Moreover, the greater the O / C molar ratio of the biochar, the better its hydrophilicity. In addition, the (O+N) / C molar ratio of the carbon-rich material can reflect the polarity of the material. The greater the (O+N) / C molar ratio of the biochar, the greater its polarity.

[0062] As can be seen from Table 2, for unmodified biochar, although the types of agricultural waste used to produce biochar are different, when carbonized at the same temperature, the aromatization degree of the obtained biochar is not different, and their hydrophilicity and polarity are also similar. Compared with unmodified biochar, the biochar modified with humic acid and calcium has higher aromaticity, hydrophilicity and polarity, indicating that the content of polar functional groups on the surface of the modified biochar is higher, and it also indicates that humic acid has been successfully grafted onto the surface of calcium-modified biochar. This conclusion is consistent with the analysis results of the infrared spectrum of humic acid-modified calcium-modified biochar in the previous text. Regarding the concentration of the modifier humic acid, as the amount of humic acid used increases, the aromaticity of the obtained modified biochar increases, while its hydrophilicity and polarity do not change significantly, indicating that an appropriate addition amount of humic acid is a necessary condition for improving the organic matter content in the modified biochar.

[0063] Table 2 Elemental analysis of humic acid-modified calcium-modified biochar and its matrix with different raw materials

[0064]

[0065] Soil saturation experiment

[0066] Select calcium humic acid-modified biochar composites labeled QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 for soil remediation experiments. The specific steps include: after mixing the soil samples with the above 4 biochar-based composites in proportion and filling them into pots, watering is carried out. After the water seeps out from the water outlet holes at the bottom of the pot, it is left standing for 12 h, and then watered again until water comes out from the bottom of the pot. Then the flower pots are placed in a greenhouse, and watered thoroughly once a week. When there is no obvious decrease in the soil body, it is in a balanced state. After reaching the balanced state, it is placed for 15 d. Thereafter, soil samples are taken every 15 d and passed through a 18-mesh sieve for measuring the physical and chemical properties of the soil. The sampling time interval for measuring the content of heavy metal ions in the soil is 30 d.

[0067] The experiment takes 4 soil remediation agents as the research objects, adopts an indoor simulation test method, and adds the soil remediation agents at one time according to 0%, 1.0%, 3.0% and 5.0% of the soil quality. And soil samples are collected on the 15th d, 30th d, 45th d and 60th d. For each soil type, 13 groups of soil samples are designed in the experiment, and each group of experimental operations is repeated 3 times. The soil sample without adding any modifier is used as the blank control group.

[0068] Change of soil pH value: During the soil remediation process, the change rules of soil pH in different treatment groups are shown in Figure 5 as follows. From Figure 5It can be seen that overall, the pH value of the soil shows an increasing trend after applying the soil remediation agent. However, the pH value of the soil without the addition of the soil remediation agent changes little during the entire incubation period and remains weakly acidic. After adding the soil remediation agent to the problematic soil, its pH value increases with the increase of the soil incubation time, and the pH value of the soil reaches the maximum after 45 days of soil incubation. In addition, it can also be seen from the figure that in terms of the types of soil remediation agents, compared with other types of soil remediation materials, the soil remediation agent QCa@PSC-600@HA-3 has a better effect on increasing the pH values of the three soils, and increasing the usage amount of the soil remediation material results in an increase in the pH value of the soil after its action. The above comprehensive analysis shows that adding soil amendments can increase the pH value of the soil to a certain extent, and among them, the soil remediation agent QCa@PSC-600@HA-3 has the most significant effect on the treatment of acidified farmland.

[0069] Change in soil electrical conductivity: During the remediation process, the change trends of the soil electrical conductivity in different treatment groups are shown in Figure 6 the figure. It can be seen from Figure 6 the figure that compared with the soil without the addition of the biochar-based composite material, the electrical conductivity of the soil in the farmland with the addition of the biochar-based composite material has decreased. In terms of different types of biochar-based composite materials, the decrease in the electrical conductivity value in the soil with the addition of QCa@PSC-600@HA-2 is the most significant, followed by QCa@MDC-600@HA-2, indicating that although the raw materials for preparing biochar are different, the change trend of their influence on the electrical conductivity in the soil is the same.

[0070] Take the biochar-based composite material QCa@PSC-600@HA-2 as an example. Its mixing dosage with the sample soil is different, and the electrical conductivity of the soil after remediation is also different. With the increase in the dosage of the biochar-based composite material, the decrease in the electrical conductivity value in the affected soil is more obvious. When the mass ratio of the biochar-based composite material to the sample soil is 1:10, the electrical conductivity value in the affected soil is the lowest, and this research result is valid for both soil samples. When QCa@PSC-600@HA-2 is applied to the sample soil at a ratio of 1:10 (w / w), its electrical conductivity value decreases significantly within 0 - 45 days, while the change in the electrical conductivity value is not obvious after more than 45 days, indicating that the biochar-based composite material can improve the fertility of degraded soil in a short time.

[0071] Change in soil organic matter content: The change trends of the organic matter content in the remediated soils of different treatment groups are shown in Figure 7 the figure. It can be seen from Figure 7It can be seen that compared with the soil without the addition of the biochar-based composite material, the organic matter content in the soil with the addition of the biochar-based composite material has increased. For different types of biochar-based composite materials, the increase in the organic matter content in the soil with the addition of QCa@PSC-600@HA-2 is the largest, followed by QCa@MDC-600@HA-2, indicating that although the raw materials for preparing biochar are different, the trend of influencing the change of the organic matter content in the soil is the same. For the biochar-based composite material QCa@PSC-600@HA-2, when its mixing dosage with the soil sample is different, the organic matter content in the repaired soil is also different.

[0072] With the increase in the dosage of the carbon-based composite material, the increase in the organic matter content in the affected soil becomes more obvious. When the mass ratio of the carbon-based composite material to the sample soil is 1:10, the organic matter content in the affected soil is the highest, and this research result is valid for both soil samples. When QCa@PSC-600@HA-2 is applied to the sample soil at a ratio of 1:10 (w / w), the increase in the soil organic matter content is relatively large within 30 days of soil incubation. After more than 45 days, the change trend of the soil organic matter content is not obvious. Since the organic matter content in the soil is an important indicator to measure the soil fertility, the biochar-based composite material can greatly increase the organic matter content in the soil in a short time, indirectly indicating that when the modified biochar is applied to the soil with degraded fertility, the effect of improvement and repair can be gradually achieved in a short time.

[0073] Change in soil urease activity: The change rule of the urease activity in the soil after repair in different groups is shown in Figure 8 as follows. It can be seen from Figure 8 that by prolonging the soil incubation time, the change in the urease activity in the control group is not obvious, while the urease activities in the soils of other groups all increase with the increase in the repair time, but the increase amplitudes of the urease activities in different groups at the same time period are different. In the initial stage of soil incubation (0 - 30 d), the increase in the urease activity in the repaired soils of groups 1-1 and 3-1 is slow. However, when the incubation time exceeds 30 d, the increase rate of the urease activity in the repaired soils of groups 2-5 and 4-5 accelerates, while the increase in the urease activity in the repaired soil of group 3-3 is the slowest. During the whole repair process, the urease activities in the repaired soils of groups 2-3 and 4-3 are always in a stable upward trend, and the numerical increase rate is the fastest.

[0074] Since the urease activity in soil is closely related to the number of microorganisms therein. When biochar-based composites are applied to the soil, the biochar interacts with the microbial community in the soil, resulting in an accelerated increase in the urease activity. Therefore, applying the biochar-based composites QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can significantly increase the number of microorganisms, and further cause an accelerated increase in the urease activity in the soil.

[0075] Changes in soil sucrase activity: During the soil incubation process, the change patterns of sucrase activity in the repaired soils of different groups are as Figure 9 shown. As Figure 9 can be seen, by prolonging the soil incubation time, the change in sucrase activity in the control group is not obvious. The sucrase activity in the repaired soils of other groups increases with the increase of the repair time, but the increase amplitudes of sucrase activity in different groups at the same time period are different. In the initial stage of soil incubation (0 - 30 d), the sucrase activity in groups 1-1 and 3-1 increases slowly. However, when the incubation time exceeds 30 d, the increase rate of sucrase activity in the repaired soils of groups 2-5 and 4-5 accelerates, while the increase rate of sucrase activity in the repaired soil of group 3-3 is the slowest. During the whole repair process, the sucrase activity in the repaired soils of groups 2-3 and 4-3 shows a stable upward trend all the time, and the numerical increase rate is the fastest. Since the sucrase activity in soil is closely related to the number of microorganisms therein. When biochar-based composites are applied to the soil, the modified biochar interacts with the microbial community in the soil, resulting in an accelerated increase in the sucrase activity. Therefore, applying the biochar-based composites QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can significantly increase the number of microorganisms, and further cause the increase rate of sucrase activity in the soil to reach the fastest.

[0076] Changes in soil alkaline phosphatase activity: The change patterns of alkaline phosphatase activity in the repaired soils of different groups are as Figure 10 shown. From Figure 10It can be seen that the changing trends of the alkaline phosphatase activities in the repaired soils of different groups are different. Regarding the soils repaired with the biochar-based composites, as the soil incubation time increases, the alkaline phosphatase activities in the repaired soils of all groups increase with the increase of the repair time. However, at the same time period, the increasing amplitudes of the alkaline phosphatase activities in the repaired soils of different groups are different. In the initial stage of soil incubation (0 - 30 d), the alkaline phosphatase activities in the repaired soils of groups 1-1 and 3-1 increase slowly. However, when the incubation time exceeds 30 d, the growth rates of the alkaline phosphatase activities in the repaired soils of groups 2-5 and 4-5 accelerate, while the growth of the alkaline phosphatase activity in the repaired soil of group 3-3 is the slowest. During the whole repair process, the alkaline phosphatase activities in the soils of groups 2-3 and 4-3 show a steady upward trend all the time, and the numerical growth rate is the fastest.

[0077] Since the alkaline phosphatase activity in the soil is closely related to the number of its microorganisms. When the biochar-based composites are applied to the test soil, the modified biochar interacts with the microbial community in the soil, resulting in an accelerated growth rate of its alkaline phosphatase activity. Therefore, applying the biochar-based composites QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can lead to the maximum alkaline phosphatase activity in the soil.

[0078] Changes in soil catalase activity: When different types and dosages of biochar-based composites are applied to the test soil, the changing trends of the catalase activities in the soil at different incubation stages are shown in Figure 11 as follows. It can be seen from Figure 11 that the changing rules of the catalase activities in the repaired soils of each treatment group are different from those of the urease, sucrase, and alkaline phosphatase activities in the soil. The catalase activity in the repaired soil of the control group is higher than that of other groups, and its enzyme activity basically does not change with the increase of the soil incubation time, while the catalase activities in the repaired soils of other groups show a decreasing trend with the increase of time. In the initial stage of soil incubation (0 - 45 d), the decreasing rates of the catalase activities in the repaired soils of groups 2-5 and 4-5 are the fastest. However, after 45 d, the decrease of the catalase activity is not obvious, indicating that the soil repair materials can reduce the catalase activity in the soil, and its decreasing rate will change with the incubation time of the soil sample. Based on the above analysis, it can be known that the pH value, organic matter content, conductivity, and enzyme activity in the soil are related to the types and dosages of the added biochar-based composites, but not related to the types of biomass used to prepare the biochar.

[0079] Content of available lead and cadmium in the soil after the remediation of problem soil: Taking soil samples No. 1 and No. 2 collected in the laboratory as research objects respectively, the effects of the types and dosages of biochar-based composites on the existing effective forms and contents of lead and cadmium elements in problem soil during different incubation periods were studied. Biochar-based composites were applied to soil sample No. 1. The available contents and their morphological distributions of Pb element and Cd element at different time periods are shown in Table 3 and Figure 12 as follows. It can be seen from Table 3 that compared with the soil without the application of biochar-based composites, after 60 days of soil incubation experiment on soil sample No. 1, the content of available Pb decreased significantly, and its content reached the lowest after 90 days of soil incubation. At the same time, the change trend of the content of available cadmium in soil No. 1 during different incubation periods was basically the same as that of available lead. In terms of different types of biochar-based composites, when QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 were respectively applied to the soil samples, their passivation effects on available Pb and Cd in the soil were better than those of other types of biochar-based composites. In terms of the addition amount of biochar-based composites, increasing the dosage of biochar-based composites decreased the contents of available Pb and Cd in the sample soil. When the addition amount of biochar-based composites reached 5% (percentage with respect to the sample soil), the contents of available Pb and Cd dropped to the lowest, basically reaching the level of the control soil sample (soil sample No. 3) in this study.

[0080] Content of available lead and cadmium in the soil after the remediation of problem soil: At the end of soil incubation, the morphological distributions of Pb and Cd in the experimental soil were analyzed respectively in the present invention. It can be seen from Figure 12 that when different types and proportions of biochar-based composites were applied to soil sample No. 1, the morphological distributions of Pb and Cd were different.

[0081] Generally speaking, compared with the soil without carbon-based composites, the content of fixed Pb in the improved sample soil number increased significantly, while the content of acid-soluble and exchangeable Pb decreased significantly. In terms of different types of biochar-based composites, QCa@MDC-600@HA-2 and QCa@MDC-600@HA-2 were respectively used to adsorb and immobilize the available lead Pb in the repaired sample soil, and their passivation abilities for Pb were almost the same.

[0082] Table 3 Available contents of Pb and Cd elements in improved soil sample No. 1 at different time periods

[0083]

[0084] Note: 1-1, 1-3, and 1-5 refer to soil samples added with soil remediation agent QCa@PSC-600@HA-1 at ratios of 1%, 3%, and 5% respectively; 2-1, 2-3, and 2-5 refer to soil samples added with soil remediation agent QCa@PSC-600@HA-2 at ratios of 1%, 3%, and 5% respectively; 3-1, 3-3, and 3-5 refer to soil samples added with soil remediation agent QCa@PSC-600@HA-3 at ratios of 1%, 3%, and 5% respectively; 4-1, 4-3, and 4-5 refer to soil samples added with soil remediation agent QCa@MDC-600@HA-2 at ratios of 1%, 3%, and 5% respectively.

[0085] Regarding different dosages of the same biochar-based composite material, during the soil incubation process, as the dosage of the biochar-based composite material increases, the content of acid-soluble and exchangeable Pb in the repaired soil decreases, while the content of fixed Pb increases. When the ratio of the biochar-based composite material to the sample soil is 1:10, the contents of acid-soluble and exchangeable Pb and fixed Pb in the repaired soil are 18.59% and 46.83% respectively. Compared with the corresponding values of the soil repaired without using the biochar-based composite material, the two are reduced by 25.87% and increased by 25.97% respectively. In addition, the effect of the biochar-based composite material on the Cd form in the repaired soil is similar to that of the Pb form. Therefore, for the soil sample repaired with the biochar-based composite material, the content of fixed Cd in it increases by 21.89% compared with the soil before repair. When the biochar-based composite material is applied to soil sample No. 2, the available content and morphological distribution of Pb and Cd elements at different time periods are shown in Table 4 and Figure 13 as follows.

[0086] It can be seen from the table that at the initial stage of soil incubation, the change trend of the available Pb content in the soil is relatively similar to that of the available Cd content, and both show varying degrees of decrease. However, when the soil incubation time exceeds 60 days, the decreasing trends of the available Pb content and the available Cd content in the soil are not obvious, and these values reach the lowest after 90 days of soil incubation. The reason for this phenomenon is that when the biochar-based composite material acts on the lead and cadmium contaminated soil, the adsorption sites on the surface of the modified biochar are basically occupied by lead and cadmium. In addition, when the biochar-based composite material acts on soil sample No. 2, its impact on the available lead and cadmium content in the soil is similar to that of soil sample No. 1, and this result is also consistent with the research conclusions on the pH value, organic matter content, conductivity, and various enzyme activities in the repaired soil, which further confirms that the soil remediation material developed in this study has potential market promotion prospects in treating farmland suffering from soil compaction and lead and cadmium pollution.

[0087] Table 4 Available content of Pb and Cd elements in improved soil sample No. 2 at different time periods

[0088]

[0089] Note: 1-1, 1-3, and 1-5 refer to the soil samples added with soil remediation agent QCa@PSC-600@HA-1 at ratios of 1%, 3%, and 5% respectively; 2-1, 2-3, and 2-5 refer to the soil samples added with soil remediation agent QCa@PSC-600@HA-2 at ratios of 1%, 3%, and 5% respectively; 3-1, 3-3, and 3-5 refer to the soil samples added with soil remediation agent QCa@PSC-600@HA-3 at ratios of 1%, 3%, and 5% respectively; 4-1, 4-3, and 4-5 refer to the soil samples added with soil remediation agent QCa@MDC-600@HA-2 at ratios of 1%, 3%, and 5% respectively.

[0090] Figure 13 It shows the morphological distribution and content change law of cadmium element at the end of soil incubation. By comparing the contents of fixed lead and fixed cadmium in the repaired soils of different groups, it can be seen that the content of fixed Cd is slightly lower than that of fixed Pb, indicating that the passivation effect of the biochar-based composite material on available lead in the soil is better than that on available cadmium. This may be due to the hydrolysis constant of Pb(II) being lower than that of Cd(II), and it is easier to be fixed by the modified biochar in the form of ion exchange.

[0091] From Figure 13 it can also be seen that when different types and ratios of biochar-based composite materials are applied to sample soil No. 2, there are slight differences in the contents of various forms of Pb and various forms of Cd. Generally speaking, compared with the soil without the application of biochar-based composite materials, the content of fixed Cd in the improved sample soil No. 2 increases significantly, while the contents of acid-soluble and exchangeable Cd decrease significantly. Regarding different types of biochar-based composite materials, QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 are respectively used to adsorb and immobilize available Cd in the repaired sample soil, and their passivation abilities for Cd are almost the same.

[0092] Regarding different dosages of the same biochar-based composite material, during the soil incubation process, as the dosage of the biochar-based composite material increases, the contents of acid-soluble and exchangeable Cd in the repaired soil decrease, while the content of fixed Cd increases. When the ratio of the biochar-based composite material to the sample soil is set to 1:10 (W / W), the contents of acid-soluble and exchangeable Cd and fixed Cd in the repaired soil are 11.23% and 38.82% respectively. Compared with the corresponding values of the soil without the application of biochar-based composite materials, the two decrease by 18.63% and increase by 21.48% respectively.

[0093] Based on the above analysis, it can be seen that there are obvious differences in the contents of various forms of Pb and various forms of Cd in the two tested soil samples. This may be related to the differences in the initial concentrations of lead and cadmium in the sample soil and the competitive adsorption between heavy metal elements on the surface of the modified biochar. Since the effects of the biochar-based composites QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 on the physical and chemical properties, available lead and cadmium contents, and their morphological distributions in the repaired soil are consistent, in order to avoid a large amount of useless work and simplify the workload, the biochar-based composites QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 are determined to be used as soil repair agents for subsequent bioavailability experiments of soil samples.

[0094] Bioavailability Evaluation of Amended Soils

[0095] According to the conclusions drawn from the aforementioned experiments, applying biochar-based composites to problematic soils can not only increase the pH value, organic matter content, and electrical conductivity of acidified soils, but also improve the activities of urease, sucrase, and alkaline phosphatase in the soils. To further evaluate the production quality of the biochar-based composites in repairing sample soils, the present invention carried out a Chinese cabbage variety experiment in the school greenhouse.

[0096] Three different biochar-based composites (QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3) were used in the experiment, and their mixing mass ratios with the sample soil were 1:5, 1:10, and 1:15 respectively. Soils without adding biochar-based composites were selected for comparison. Based on the growth and quality indicators of Chinese cabbage in the pot experiment, the repair ability of the prepared biochar-based composites to the selected problematic soils was evaluated. The contents and morphological distributions of available Pb and available Cd in the sample soil and Chinese cabbage plants were studied respectively. Finally, the action mechanism of the biochar-based composites in repairing soil compaction and lead- and cadmium-polluted farmland was explored.

[0097] Two types of problematic soils collected were used as the research objects in the experiment. By applying different types and concentrations of biochar-based composites to them and planting Chinese cabbage on them, the growth conditions of Chinese cabbage, the physical and chemical properties of the soil, and the heavy metal contents in them were observed. The detailed experimental steps are described as follows:

[0098] The biochar-based composite materials were mixed with the test soil at ratios of 1:5 (w / w), 1:10 (w / w), and 1:15 (w / w) respectively, and then filled into flower pots. The carefully selected pakchoi seeds were evenly sown into each flower pot, with 18 pakchoi seeds sown in each pot experiment. Before the seeds germinated, water was poured once every other day. After the seeds germinated, water was poured once a day, and it was ensured that the soil in the pakchoi pots remained moist. The germination rate of the pakchoi seeds was observed regularly. Thinning of the pakchoi seedlings began 16 days after sowing. After the pakchoi had grown for 36 days, the pakchoi was pulled out from the planted pakchoi pots, and the growth index of the pakchoi plants in each group of pots was observed.

[0099] Two small plots of land were found in the school greenhouse, and the test soil collected from the field was simulated respectively. Using the biochar-based composite material QCa@PSC-600@HA-2 as a soil remediator, it was mixed and incubated with two kinds of simulated soils (soil sample No. 1 and soil sample No. 2) at a mass ratio of 1:10 respectively. After 90 days, pakchoi was planted on them respectively. After the pakchoi had grown for 30 days, the growth status of the pakchoi was observed and the heavy metal contents in the soil and pakchoi plants were determined.

[0100] By conducting a pakchoi planting experiment in the greenhouse and dynamically monitoring the growth indexes (germination rate, fresh weight and dry weight of plants, plant height) and quality indexes (chlorophyll, soluble protein and soluble sugar) of pakchoi planted in the soil incubated with the biochar-based composite material, the effect of the soil remediator on the growth status of pakchoi was studied.

[0101] Effect on the growth of pakchoi: Figure 14 are the physical pictures of pakchoi planted in the soil before and after being remediated by the biochar-based composite material. From Figure 14 it can be seen that generally speaking, compared with the pakchoi plants in the soil without the application of the biochar-based composite material for remediation, the pakchoi plants in the soil with the application of the biochar-based composite material grew better; moreover, when the same type and the same concentration of biochar-based composite material were applied to soil sample No. 1 and soil sample No. 2 respectively, the pakchoi plants planted grew well. In terms of different types of biochar-based composite materials, QCa@PSC-600@HA-2 as a soil remediator was better than QCa@PSC-600@HA-1 and QCa@PSC-600@HA-3 in terms of the plant height and leaf greenness of pakchoi.

[0102] This indicates that during the preparation of modified biochar, an appropriate amount of HA is beneficial for the biochar surface to immobilize more oxygen-containing groups. Moreover, as the dosage of the soil remediation agent increases, the heights of the pakchoi plants in the repaired soil samples No. 1 and No. 2 both increase. This shows that in the soil applied with the biochar-based composite material, the modified biochar and its surface humic acid both contribute to improving the soil air permeability, electrical conductivity, and organic matter content, thereby alleviating the soil compaction degree and promoting the growth of pakchoi.

[0103] The biological trait parameters of pakchoi (such as germination rate, plant fresh weight, plant dry weight, plant height, etc.) can reflect its growth situation. Table 5 lists the biological trait parameters of pakchoi in the soil repaired by different soil remediation agents.

[0104] The changes in the soil environment can directly affect plant growth. Table 5 lists the biological trait parameters of pakchoi after 36 days of planting. It can be seen from the table that compared with the soil without the biochar-based composite material applied, the germination rate of pakchoi in the soil repaired by the biochar-based composite material has increased significantly. Regarding different types of biochar-based composite materials, when adding QCa@PSC-600@HA-2 to the test soil at a ratio of 1:10 (w / w), the germination rate of pakchoi planted on it is relatively high, followed by that of pakchoi planted in the soil treated with QCa@PSC-600@HA-3 at the same ratio. Regarding the dosage of the same biochar-based composite material, when applying the carbon-based composite material to the test soil at a mass ratio of 1:10, the germination rate of pakchoi is relatively high; when the mass ratio of the two decreases to 1:15, the germination rate of pakchoi in the repaired soil is relatively low, indicating that the dosage of the soil remediation agent has a significant impact on improving the fertilizer efficiency of degraded soil.

[0105] Table 5 Biological trait parameters of pakchoi

[0106]

[0107] Note: 1-1, 2-1, and 3-1 are adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil sample No. 1 at a ratio of 1:5 (w / w) respectively; 2-1, 2-2, and 2-3 are adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil sample No. 1 at a ratio of 1:10 (w / w) respectively; 3-1, 3-2, and 3-3 are adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil sample No. 1 at a ratio of 1:15 (w / w) respectively.

[0108] In addition, compared with the unrepaired sample soil, the fresh weight, dry weight, and plant height of pakchoi grown in the improved sample soil all increased. For different types of biochar-based composites, when adding QCa@PSC-600@HA-2 to the sample soil at a ratio of 1:10 (w / w), the increases in the fresh weight, dry weight, and plant height of pakchoi grown on it reached 99.6%, 113.8%, and 146.1% respectively. The increases in the fresh weight, dry weight, and plant height of pakchoi in the soil treated with QCa@PSC-600@HA-1 were relatively small. Regarding the dosage of the same biochar-based composite, the highest increases in the fresh weight, dry weight, and plant height of pakchoi were in the soil to which the carbon-based composite was applied at a mass ratio of 1:10 to the sample, while the increases in the fresh weight, dry weight, and plant height of pakchoi in the soil to which the repair agent was applied at a mass ratio of 1:5 were the smallest. This result is the same as that of the pakchoi germination rate.

[0109] In addition, the ability of the biochar-based composite to improve sample 2 soil was almost the same as that of sample 1 soil, indicating that the developed humic acid-modified calcium-modified biochar soil repair agent has universality in the ability to improve problematic soils.

[0110] Effect on the quality of pakchoi: To further explore the repair effect of the biochar-based composite on compacted and heavy metal-polluted soil, by measuring the physiological and biochemical indexes of pakchoi in the repaired soil (such as chlorophyll, soluble sugar, and protein), the ability of the biochar-based composite to improve problematic soil was indirectly reflected. The relevant test results are shown in Figure 15 、 Figure 16 and Figure 17 as shown. The chlorophyll content of pakchoi in the soil repaired with different concentrations and different types of biochar-based composites is shown in Figure 15 as shown. It can be seen from the figure that in the pakchoi planting experiment of soil sample No. 1, compared with pakchoi grown in the soil without applying the biochar-based composite, the chlorophyll content in the leaves of pakchoi in the improved soil increased, and the increase amplitude was as high as 124.68%.

[0111] For different types of biochar-based composites, the chlorophyll content in pakchoi grown in soil modified by QCa@PSC-600@HA-2 is higher than that of other types. By comparing the chlorophyll content of pakchoi in soil treated with the same type of biochar-based composite at different doses, it is found that the chlorophyll content increases with the increase in the amount of modified biochar. The change rule of chlorophyll content obtained from the pakchoi planting experiment in soil sample No. 1 is consistent with that in the pakchoi planting experiment in soil sample No. 2. Of course, during the soil remediation process, the amount of biochar is not the more the better, and this phenomenon has been verified in the determination of chlorophyll content in pakchoi planted in both soil samples. When the mass ratio of the biochar-based composite to the sample soil is 1:10, the chlorophyll content of pakchoi in the modified soil reaches the maximum, and the chlorophyll contents of pakchoi in soil sample No. 1 and soil sample No. 2 are 2.53 mg / g and 2.62 mg / g, respectively.

[0112] Effect on the soluble protein content in pakchoi plants: Among them, the soluble protein content of pakchoi in soil treated with biochar-based composites at different concentrations and of different types is shown in Figure 16 as follows. From Figure 16 it can be seen that in the pakchoi planting experiment in soil sample No. 1, compared with pakchoi in soil without biochar-based composite, the soluble protein content in the leaves of pakchoi in the modified soil has increased, and the increase rate is as high as 32.87%. For different types of biochar-based composites, the soluble protein content of pakchoi in soil modified by QCa@PSC-600@HA-2 is higher than that of other types. By comparing the soluble protein content of pakchoi in the repaired soil with the same type of biochar-based composite at different doses, it is found that the soluble protein content can increase with the increase in the amount of modified biochar. The change rule of the soluble protein content obtained from the pakchoi planting experiment in soil sample No. 1 is consistent with that in the pakchoi planting experiment in soil sample No. 2. Of course, during the soil remediation process, the amount of biochar-based composite is not the more the better, and this phenomenon has been verified in the determination of the soluble protein content of pakchoi in both soil samples. When the mass ratio of the biochar-based composite to the sample soil is 1:10, the soluble protein content of pakchoi grown in the modified soil is the highest, and the chlorophyll contents of pakchoi in soil sample No. 1 and No. 2 are 27.69 mg / g and 28.92 mg / g, respectively.

[0113] Effect on the soluble sugar content in pakchoi plants: The soluble sugar content of pakchoi in soil repaired by biochar-based composites at different concentrations and of different types is shown in Figure 17 as follows. From Figure 17It can be seen that overall, in the pakchoi planting experiment with soil sample No. 1, the biochar-based composite material has little correlation with the soluble sugar content of pakchoi in the repaired soil. For the sample soils treated with biochar-based composite materials of the same dose and different types, the soluble sugar content of pakchoi planted on them shows no regularity. However, when comparing the sample soils treated with biochar-based composite materials of the same type and different dosages, the changes in the soluble sugar content in the harvested pakchoi leaves basically do not show regularity. Moreover, the soluble sugar content of pakchoi planted in soil sample No. 1 and soil sample No. 2 treated with biochar-based composite materials of the same type and the same dose is not much different, indicating that the soluble sugar content in plants is not only affected by the nutrients in the soil, but also the growth environment has a great impact on its soluble sugar content.

[0114] Content and morphological distribution of available lead and cadmium in the soil after pakchoi maturity: Given that no heavy metals were detected in the pakchoi grown in two small experimental fields simulating the externally collected soil in the school greenhouse, the experiment also measured the content and morphological distribution of available lead and cadmium in the soil of the simulated plots before and after applying the soil remediation agent. The relevant test results are shown in Table 7 and Figure 18 as shown. The content of available lead and cadmium in the soil of the simulated plot before and after pakchoi harvest after being repaired with the biochar-based composite material QCa@PSC-600@HA-2 for 90 days is listed in Table 6.

[0115] Table 6 Content of available Pb and available Cd in the soil before and after pakchoi planting

[0116]

[0117] As can be seen from Table 6, when pakchoi is planted in soil sample No. 1 repaired with the biochar-based composite material, comparing the content of available Pb in the soil before and after pakchoi harvest, the numerical changes between the two are not obvious, indicating that the available lead in the soil has not transferred to the pakchoi plants. The reason for this phenomenon is that when humic acid-modified calcium-modified biochar is applied to the sample soil, the polar oxygen-containing groups on the biochar surface may adsorb and complex with some heavy metals in the soil, thereby achieving the purpose of passivating heavy metals. Moreover, oxygen-containing acid root ions such as PO4 3- and CO3 2- in the soil may also react with lead and cadmium ions to form precipitates.

[0118] In addition, the difference in the available Cd content in the soil before and after the planting and harvesting of pakchoi was not significant, indicating that the available Cd in the soil was not transferred to the pakchoi plants. In addition, pakchoi was planted in Soil Sample No. 1 and Soil Sample No. 2 that had been repaired with the biochar-based composite material, and the difference in the available lead content in the soil before sowing and after harvesting was also not significant. Since no available lead and available cadmium were detected in the harvested pakchoi plants in this study, the accuracy of the experimental results was verified. Pakchoi was planted in Soil Sample No. 1 that had been repaired with the biochar-based composite material, and the morphological distributions of Pb (or / and Cd) in the soil before and after the planting of pakchoi were measured respectively. The relevant results are shown in Figure 18 as follows.

[0119] As can be seen from Figure 18 , for Soil Sample No. 1 that had been repaired with the biochar-based composite material, comparing the content of fixed Pb in the soil before sowing and after harvesting of pakchoi, it was found that the changes were not significant, and the differences in the contents of other forms of Pb (such as acid-soluble and exchangeable Pb, oxidized Pb, and reduced Pb) were also not obvious. At the same time, the differences in the contents of various forms of Cd in the soil before sowing and after harvesting of pakchoi were also not significant. In summary, during the growth of pakchoi, the available lead and available cadmium in the soil were not transferred to the pakchoi plants. In addition, pakchoi was planted in Soil Sample No. 2 that had been repaired with the biochar-based composite material, and the contents of available lead and cadmium in the soil before sowing and after harvesting of pakchoi did not change significantly.

[0120] Analysis of the mechanism of action of biochar-based composite materials in repairing compacted and heavy metal-polluted soils: Applying humic acid-modified calcium-modified biochar to farmland suffering from soil compaction and heavy metal pollution, there are interactions between biochar and anions, cations, heavy metals, microorganisms, etc. in the soil. When the biochar-based composite material enters the heavy metal-polluted soil, the negative charges and polar oxygen-containing functional groups on its surface respectively have electrostatic adsorption effects with lead ions and cadmium ions carrying positive charges. Moreover, the surface of calcium-modified biochar contains a large number of inorganic mineral ions (such as Ca 2+ ) and oxygen-containing anions, all of which can undergo ion exchange reactions with heavy metal ions (such as lead and cadmium) in the soil, thereby inhibiting the migration and transfer of heavy metal ions in the soil.

[0121] Meanwhile, the surface of humic acid-modified biochar contains a large number of polar oxygen-containing groups (such as hydroxyl groups, carboxyl groups, carbonyl groups, etc.), which can achieve the purpose of immobilization by oxidizing heavy metals such as lead and cadmium. In addition, biochar with a high specific surface area and a developed pore structure has more adsorption sites on its surface or in the pores, and can immobilize heavy metals on the surface or inside the pores of biochar through intermolecular forces, thereby achieving the effect of passivating heavy metals. When humic acid-modified calcium-modified biochar acts on compacted soil, the abundant oxygen-containing groups on its surface increase the soil pH value, and at the same time, increase the organic matter content and decrease the conductivity in the soil. The introduction of biochar changes the community structure of microorganisms in the soil, increases the activities of urease, sucrase and alkaline phosphatase in the soil, and thus achieves the purpose of soil carbon sequestration and stabilizing the nitrogen and phosphorus contents. In addition, the surface of biochar prepared from waste mushroom stick residues contains a large number of inorganic mineral ions. When it enters the soil, it improves the cation exchange capacity in the soil and enhances the water retention capacity of the soil, reducing the compactness of the soil.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements on some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. A preparation method of modified mushroom stick biochar, comprising the following steps: Preparing biochar: Carbonizing the lignin - removed mushroom stick residue to obtain biochar; Preparing calcium - modified biochar: Mixing the biochar with calcium chloride solution, filtering, then drying, grinding, and sieving to obtain calcium - modified biochar; Preparing modified mushroom stick biochar: Mixing the calcium - modified biochar with humic acid, placing it in deionized water, stirring and reacting, then filtering. The filter residue is air - dried to obtain modified mushroom stick biochar, wherein the mass ratio of the calcium - modified biochar to the humic acid is (5 - 19):

1.

2. The preparation method of a modified mushroom stick biochar according to claim 1, characterized in that: The step of preparing biochar specifically includes: Washing the mushroom stick residue with deionized water, drying, then crushing and sieving. The obtained mushroom stick residue powder is stirred in NaOH solution for 3 h - 8 h to remove the lignin in the mushroom stick residue powder components. After filtering, grinding, and sieving, carbonization treatment is carried out for 1 h - 3 h under the conditions of N2 atmosphere, carbonization temperature of 400 °C - 800 °C, and heating rate of 3 °C / min - 10 °C / min to obtain the biochar.

3. The preparation method of a modified mushroom stick biochar according to claim 1 or 2, characterized in that: The step of preparing calcium - modified biochar specifically includes: Adding the biochar to calcium chloride solution according to the standard of adding 2 g - 10 g of the biochar per 50 mL of calcium chloride solution, stirring at room temperature for 12 h - 24 h, then filtering the reaction solution. The obtained filter residue is washed with deionized water and then dried at a temperature of 80 °C - 120 °C. The obtained black solid is ground and sieved to obtain the calcium - modified biochar.

4. An application of modified mushroom stick biochar as a soil remediator in soil remediation.

5. Use of the modified fungus stick biochar as claimed in claim 4 as a soil remediation agent for soil remediation, characterized in that: When the modified mushroom stick biochar can be used as a soil remediator for soil remediation, the mass ratio of the modified mushroom stick biochar to the soil is 1:(5 - 15).

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