Sludge, bagasse and calcium oxide co-pyrolysis biochar as soil additive and preparation method and application thereof

Abstract

The invention discloses a sludge, bagasse and calcium oxide co-pyrolysis biochar as a soil additive, and a preparation method and application thereof, and belongs to the technical field of environmental restoration. Sludge biochar synergistically modified by bagasse and calcium oxide is used as a soil additive, calcium oxide is introduced for catalytic co-pyrolysis through the synergistic effect of bagasse and calcium oxide, and sludge-bagasse-calcium oxide biochar is prepared; the optimization effect of the sludge-bagasse-calcium oxide biochar in heavy metal contaminated soil remediation is evaluated through heavy metal occurrence form analysis, ecological risk assessment and soil remediation effect experiments. According to the sludge-bagasse-calcium oxide biochar prepared by the method, the fixing capacity of the biochar on heavy metals and the fixing efficiency of the heavy metals in soil are improved, and the physicochemical properties and fertility characteristics of the heavy metal contaminated soil are improved; the characteristics of the sludge-bagasse-calcium oxide biochar for well fixing heavy metals and improving soil properties are exerted, the ecological risk is reduced, the physicochemical properties and fertility characteristics of the soil are improved, and the application of a heavy metal contaminated soil remediation process is optimized.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental remediation, and particularly relates to a co-pyrolysis biochar of sludge, bagasse, and calcium oxide as a soil additive, as well as a preparation method and application thereof. Background Art

[0002] Sludge contains toxic substances such as bacteria, parasites, organic matter, and heavy metals, presenting significant ecological and environmental risks. Improper disposal or storage of sludge can lead to serious secondary pollution. In the process of sludge resource utilization, pyrolysis technology, as an effective sludge treatment method, can achieve sludge reduction, stabilization, harmlessness, and resource utilization. However, the high moisture and ash content of sludge pose challenges such as high energy consumption, low carbon yield, and poor chemical stability during pyrolysis. Moreover, most heavy metals accumulate in sludge biochar after pyrolysis, and volatile organic compounds in sludge also affect the formation and size distribution of pores in sludge biochar. These problems reduce its adsorption and storage capacity and limit its potential uses in the agricultural and environmental fields.

[0003] Harmful heavy metals such as cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) are commonly present in heavy metal-contaminated soils. These heavy metals mostly originate from industrial emissions, mining, and agricultural activities and easily threaten the ecosystem and human health through biological enrichment. Moreover, heavy metal-contaminated soils usually show degradation of soil properties, such as high salinization degree, weak cation exchange capacity, low organic matter content, and soil compaction.

[0004] Therefore, the present invention attempts to provide a process for optimizing the remediation effect of heavy metal-contaminated soils, reducing the content of available heavy metals in the soil, improving the physical and chemical properties of the soil, and enhancing the soil fertility characteristics. Co-pyrolyzing sludge with bagasse and calcium oxide reduces the heavy metal content in the soil, increases the carbon content of the biochar, promotes the transformation of heavy metals in the sludge into more stable forms, and enhances its environmental safety. This technology provides an efficient and low-risk solution for sludge resource utilization. This method provides an efficient and sustainable solution for the remediation and fertility improvement of heavy metal-contaminated soils. Summary of the Invention

[0005] This study aims to explore the synergistic effect of sludge, bagasse, and calcium oxide on the remediation of heavy metal-contaminated soils and the application potential of improving soil properties. Therefore, the present invention provides a co-pyrolysis biochar of sludge, bagasse, and calcium oxide as a soil additive, as well as a preparation method and application thereof.

[0006] A preparation method of a co-pyrolysis biochar of sludge, bagasse, and calcium oxide as a soil additive includes the following steps:

[0007] (1) Dry and grind the sludge and bagasse, then screen them, and then mix them with calcium oxide to obtain a mixture;

[0008] (2) Pyrolyze the mixture obtained in step (1) under a nitrogen atmosphere, and after cooling, perform screening to obtain sludge - bagasse - calcium oxide biochar.

[0009] As this implementation plan, in step (1), the mass ratio of sewage sludge to bagasse is 1:1. After drying and grinding, the sludge and bagasse are respectively sieved through a 60 - mesh sieve and a 20 - mesh sieve, and the addition amount of calcium oxide is 30% of the total mass of the mixture.

[0010] As this implementation plan, in step (2), the temperature of the pyrolysis is 600 - 750 °C, the pyrolysis time is 1 - 2 h, and a biochar sample is obtained after cooling.

[0011] The method described in the present invention is used to prepare sludge, bagasse, and calcium oxide co - pyrolyzed biochar.

[0012] Regarding the application of the sludge, bagasse, and calcium oxide co - pyrolyzed biochar described in the present invention in the remediation of heavy - metal - contaminated soil, the evaluation method includes the following steps:

[0013] (1) Apply the sludge - bagasse - calcium oxide biochar to the heavy - metal - contaminated soil according to the mass ratio, conduct cultivation for 49 days, and sample and dry for preservation every 7 days for later use.

[0014] (2) Determine the contents of available heavy metals (DTPA - Cd, DTPA - Cu, DTPA - Ni, DTPA - Pb, DTPA - Zn, etc.) in the soil, and evaluate the influence of the sludge - bagasse - calcium oxide biochar on the available heavy metals in the soil.

[0015] (3) Determine the contents of soil pH, electrical conductivity (EC), and cation exchange capacity (CEC), and evaluate the influence of the sludge - bagasse - calcium oxide biochar on the physical and chemical properties of the soil.

[0016] (4) Determine the contents of soil organic matter (OM), total nitrogen (TN), available potassium (AK), and available phosphorus (AP), and evaluate the influence of the sludge - bagasse - calcium oxide biochar on the soil fertility characteristics.

[0017] As this implementation plan, in step (1), the addition amount of the sludge - bagasse - calcium oxide biochar is 2% - 6% of the total mass of the soil sample. The heavy - metal - contaminated soil without adding the sludge - bagasse - calcium oxide biochar is used as the blank control group. After mixing evenly, put it into flowerpots, and air - dry the collected soil samples and sieve them through a 20 - mesh sieve for preservation for later use.

[0018] As this implementation plan, in step (2), the determination of the available heavy metal content in the soil is carried out according to the standard of "Determination of 8 available elements in soil - Extraction with diethylenetriaminepentaacetic acid - Inductively coupled plasma optical emission spectrometry" (HJ 804 - 2016).

[0019] As for this implementation scheme, the soil pH and electrical conductivity (EC) in step (3) are measured using a pH meter and an electrical conductivity meter, and the cation exchange capacity (CEC) content is measured with reference to "Determination of Cation Exchange Capacity of Soils - Extraction with Hexaamminecobalt(III) Chloride - Spectrophotometry" (HJ 889-2017).

[0020] As for this implementation scheme, the soil organic matter (OM), total nitrogen (TN), available potassium (AK), and available phosphorus (AP) in step (4) are measured using an automatic organic matter analyzer, a Kjeldahl nitrogen analyzer, an ICP-OES, and an ultraviolet-visible spectrophotometer, respectively.

[0021] The preparation method and application of the sludge-bagasse-calcium oxide biochar co-pyrolysis biochar as a soil additive in the present invention are that the sludge-bagasse-calcium oxide biochar is used as a heavy metal contaminated soil additive to reduce soil heavy metal pollution and improve soil properties. The sludge-bagasse-calcium oxide biochar has the ability to adsorb heavy metals in the soil, improve soil physical and chemical properties, and enhance soil fertility characteristics. After adding the sludge-bagasse-calcium oxide biochar to the heavy metal contaminated soil, the content of available heavy metals in the soil is reduced, the soil acidity, alkalinity, and salinity are improved, the soil water and fertilizer retention capacity is enhanced, and the soil fertility characteristics are significantly improved, showing a significant optimization effect in the remediation and fertility improvement of heavy metal contaminated soil.

[0022] To achieve the above object, the technical solutions adopted specifically include the following steps:

[0023] (1) Treatment of biochar raw materials: The sludge used in the experiment was taken from Luolong Sewage Treatment Plant in Kunming, Yunnan Province, China, and the bagasse was taken from Maoming City, Guangdong Province, China. The sludge and bagasse were dried at 105°C, ground, and then the sludge and bagasse were passed through 60-mesh and 20-mesh sieves respectively for standby.

[0024] (2) Preparation of biochar: Take a certain amount of dry sludge, bagasse, and calcium oxide, use a ball mill to mix them evenly according to the set mass ratio, and then place them in a tubular furnace. Pyrolyze at a pyrolysis temperature of 600-750°C for 1-2 h under a nitrogen atmosphere. Among them, N2 is introduced at a constant flow rate of 180 mL / min, the furnace temperature of the tubular furnace is raised to 600°C at a heating rate of 5°C / min and maintained for 60 min, and then the temperature is raised to 750°C at a heating rate of 5°C / min and maintained for 60 min, and then the tubular furnace is closed. After natural cooling, the pyrolysis product is collected, which is the sludge-bagasse-calcium oxide biochar.

[0025] (3) Soil experiment: The heavy metal-contaminated soil used in the experiment was taken from a wet copper smelting base in Yuxi City, Yunnan Province, China. It was air-dried at room temperature and passed through a 20-mesh sieve for standby. The sludge-bagasse-calcium oxide biochar was added to the heavy metal-contaminated soil samples at ratios of 2%, 4%, and 6% by total mass of the soil samples. The heavy metal-contaminated soil without the addition of sludge-bagasse-calcium oxide biochar served as the blank control group. After the samples were mixed evenly, they were transferred into flower pots, and gauze and filter paper were laid at the bottom of the flower pots to prevent soil loss. During the experiment, the soil moisture content was maintained at 70% of the field capacity. The entire experimental period lasted for 49 days. Samples were collected from each flower pot at 0, 7, 14, 21, 28, 35, 42, and 49 days, air-dried, and passed through a 20-mesh sieve for the determination of the content of available heavy metals, pH value, electrical conductivity (EC), cation exchange capacity (CEC), organic matter (OM), total nitrogen (TN), available potassium (AK), and available phosphorus (AP) in the samples, so as to study the properties of the heavy metal-contaminated soil after the addition of biochar.

[0026] (4) Determination of the content of available heavy metals in soil: The available heavy metals in soil samples were determined with reference to "Determination of 8 available elements in soil - Extraction with diethylenetriaminepentaacetic acid - Inductively coupled plasma optical emission spectrometry" (HJ 804-2016). Each available element in the soil was extracted with a diethylenetriaminepentaacetic acid-calcium chloride-triethanolamine (DTPA-CaCl2-TEA) buffer solution, and the contents of DTPA-Cd, DTPA-Cu, DTPA-Ni, DTPA-Pb, and DTPA-Zn in the extract were determined by ICP-MS.

[0027] (5) Determination of soil physical and chemical properties: The pH, electrical conductivity (EC), and cation exchange capacity (CEC) of soil samples were measured using a pH meter, a conductivity meter, and a portable redox potential meter respectively, and the determination of cation exchange capacity in soil was carried out with reference to "Determination of cation exchange capacity in soil - Extraction with hexaamminecobalt(III) chloride - Spectrophotometry" (HJ 889-2017).

[0028] (6) Determination of soil fertility characteristics: The content of organic matter (OM) was determined using a fully automatic organic matter analyzer with reference to "Soil testing - Part 6: Determination of soil organic carbon and organic matter" (NY / T 1121.6-2006). The content of total nitrogen (TN) was determined using a fully automatic Kjeldahl distiller with reference to (NY / T1121.24-2012); the content of available potassium (AK) was determined by ICP-OES with reference to "Available potassium and slow-release potassium in soil" (NY / T 889-2004); the content of available phosphorus (AP) was determined using an ultraviolet-visible spectrophotometer with reference to "Soil testing - Part 7: Determination of available phosphorus in soil" (NY / T 1121.7-2014).

[0029] The method of using sludge - bagasse - calcium oxide biochar as a soil additive to improve the remediation efficiency of heavy metal - contaminated soil shows excellent performance in the application of heavy metal - contaminated soil remediation technology.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) In the present invention, solid waste sludge and bagasse are dried and screened and then mixed, and calcium oxide is introduced for catalytic co - pyrolysis, which significantly improves the heavy metal fixation ability of biochar. The present invention not only reduces the raw material cost but also reduces the potential harm of waste to the environment, meeting the concepts of environmental protection and sustainable development.

[0032] (2) Using sludge - bagasse - calcium oxide biochar as a soil additive improves the physical and chemical properties of the soil. The soil is improved from acidic soil to neutral and alkaline soil, significantly reducing the soil salinization degree, enhancing the water retention and air permeability of the soil, and significantly improving the fertility characteristics of the soil. The organic matter content increases from 8.74 to 27.10 g / kg, the total nitrogen content increases from 0.364 to 0.583 g / kg, the available potassium content increases from 45.00 to 109.00 mg / kg, and the available phosphorus content increases from 5.60 to 113.00 mg / kg.

[0033] (3) The sludge - bagasse - calcium oxide biochar soil additive prepared in the present invention significantly reduces the content of available heavy metals in heavy metal - contaminated soil. The concentration limits of DTPA - Cd, DTPA - Cu, DTPA - Ni, DTPA - Pb, and DTPA - Zn in the soil samples added with biochar are reduced by 15.75% - 69.82%, indicating that the sludge - bagasse - calcium oxide biochar has an effective passivation effect on heavy metals in the soil, which is of great significance for reducing the ecological environment risk. It is applicable to the remediation of various heavy metal - contaminated soils, and the raw materials are all common solid wastes, which are easy to obtain and low in cost, and are easy to promote. It realizes the efficient resource utilization of waste and can be widely applied to scenarios such as farmland and mining areas that require land remediation, with significant environmental protection and social benefits. Description of the Drawings

[0034] Figure 1For Application Example 1, the changes in the content of available heavy metals in heavy metal-contaminated soil with different ratios of sludge-bagasse-calcium oxide biochar. Figure (a) shows the change in the content of available heavy metal DTPA-Cd in heavy metal-contaminated soil, Figure (b) shows the change in the content of available heavy metal DTPA-Cu in heavy metal-contaminated soil, Figure (c) shows the change in the content of available heavy metal DTPA-Ni in heavy metal-contaminated soil, Figure (d) shows the change in the content of available heavy metal DTPA-Pb in heavy metal-contaminated soil, and Figure (e) shows the change in the content of available heavy metal DTPA-Zn in heavy metal-contaminated soil.

[0035] Figure 2 For Application Example 2, the changes in the physical and chemical properties of heavy metal-contaminated soil at different times under different ratios of sludge-bagasse-calcium oxide biochar conditions. Figure (a) shows the change in the physical and chemical property pH of heavy metal-contaminated soil, Figure (b) shows the change in the electrical conductivity (EC) of heavy metal-contaminated soil, and Figure (c) shows the change in the cation exchange capacity (CEC) of heavy metal-contaminated soil.

[0036] Figure 3 For Application Example 3, the changes in the fertility properties of heavy metal-contaminated soil at different times under different ratios of sludge-bagasse-calcium oxide biochar conditions. Figure (a) shows the change in the fertility property organic matter (OM) of heavy metal-contaminated soil, Figure (b) shows the change in the total nitrogen (TN) of heavy metal-contaminated soil, Figure (c) shows the change in the available potassium (AK) of heavy metal-contaminated soil, and Figure (d) shows the change in the content of available phosphorus (AP) of heavy metal-contaminated soil. Detailed implementation manners

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the described content. Any transformation based on the teachings of the present invention falls within the protection scope of the present invention.

[0038] Embodiment 1

[0039] A preparation method of sludge, bagasse, and calcium oxide co-pyrolysis biochar as a soil additive, comprising the following steps:

[0040] (1) Treatment of biochar raw materials: The sludge used in the experiment was taken from Luolong Sewage Treatment Plant in Kunming, Yunnan Province, China, and the bagasse was taken from Maoming, Guangdong Province, China. The sludge and bagasse were dried at 105 °C, ground, and then the sludge and bagasse were respectively passed through a 60-mesh sieve and a 20-mesh sieve for standby.

[0041] (2) Preparation of biochar: Take a certain amount of dry sludge, bagasse, and calcium oxide. Use a ball mill to mix them evenly according to the set mass ratio, then place them in a tube furnace. Pass in N2 at a constant flow rate of 180 mL / min. Raise the temperature of the tube furnace to 600 °C at a heating rate of 5 °C / min and hold for 60 min. Then, raise the temperature to 750 °C at a heating rate of 5 °C / min and hold for 60 min. After that, turn off the tube furnace. Wait for natural cooling and collect the pyrolysis product, which is the sludge-bagasse-calcium oxide biochar. Pass it through a 100-mesh sieve and reserve for use.

[0042] Comparative Example 1

[0043] A preparation method of a co-pyrolysis biochar of sludge and bagasse as a soil additive includes the following steps:

[0044] (1) Treatment of biochar raw materials: The sludge used in the experiment was taken from Luolong Sewage Treatment Plant in Kunming, Yunnan Province, China, and the bagasse was taken from Maoming City, Guangdong Province, China. The sludge and bagasse were dried at 105 °C, ground, and then passed through a 60-mesh sieve and a 20-mesh sieve respectively for reserve.

[0045] (2) Preparation of biochar: Take a certain amount of dry sludge and bagasse. Use a ball mill to mix them evenly according to the set mass ratio, then place them in a tube furnace. Pass in N2 at a constant flow rate of 180 mL / min. Raise the temperature of the tube furnace to 600 °C at a heating rate of 5 °C / min and hold for 60 min. Then, raise the temperature to 750 °C at a heating rate of 5 °C / min and hold for 60 min. After that, turn off the tube furnace. Wait for natural cooling and collect the pyrolysis product, which is the sludge-bagasse biochar. Pass it through a 100-mesh sieve and reserve for use.

[0046] Due to the lack of the synergistic regulation of calcium oxide, the sludge-bagasse biochar in Comparative Example 1 has poor effects on passivating heavy metals and improving soil physical and chemical properties. First, the biochar prepared by adding calcium oxide can further enhance the remediation performance of biochar through multi-path synergistic effects (pH regulation, heavy metal fixation, nutrient retention) during the co-pyrolysis process. Second, the sludge-bagasse-calcium oxide biochar reacts with the acid radical ions in the soil, which can simultaneously reduce the soil soluble salt content and the electrical conductivity (EC) in the soil, thereby increasing the soil pH and promoting the formation of hydroxide or carbonate precipitates of heavy metals to reduce the content of available heavy metals. The single sludge-bagasse biochar has limited improvement on the soil pH because calcium oxide can promote the formation of oxygen-containing functional groups on the biochar surface, enhance the cation exchange capacity, and to a certain extent affect the soil heavy metal fixation efficiency. In addition, since both sludge and bagasse are raw materials rich in organic matter, these organic matters are converted into a part of the biochar during the co-pyrolysis process. The addition of calcium oxide helps to retain nutrients during its pyrolysis process, resulting in an insignificant improvement effect of the sludge-bagasse biochar on the CEC in the soil and a decrease in the nutrient retention rate.

[0047] Application Example 1

[0048] A method and application of using the co-pyrolysis biochar of sludge, bagasse and calcium oxide as a soil additive to reduce the content of available heavy metals in heavy metal contaminated soil. The co-pyrolysis biochar of sludge, bagasse and calcium oxide is applied to heavy metal contaminated soil to study its effect on the content of available heavy metals in heavy metal contaminated soil. The method is as follows:

[0049] (1) Soil experiment: The sludge, bagasse and calcium oxide biochar prepared in Example 1 were applied to heavy metal contaminated soil. The heavy metal contaminated soil used in the experiment was taken from the wet copper smelting base in Yuxi City, Yunnan Province, China, air-dried at room temperature, and passed through a 20-mesh sieve for standby. The sludge-bagasse-calcium oxide biochar was added to the heavy metal contaminated soil samples at ratios of 2%, 4%, and 6% of the total mass of the soil samples. The sample without adding sludge-bagasse-calcium oxide biochar was used as the heavy metal contaminated soil blank control group. After the samples were mixed evenly, they were transferred to flower pots. Gauze and filter paper were laid at the bottom of the flower pots to prevent soil loss. During the experiment, the soil moisture content was maintained at 70% of the field capacity. The entire experimental period lasted for 49 days. Samples were collected from each flower pot at 0, 7, 14, 21, 28, 35, 42, and 49 days, air-dried, and passed through a 20-mesh sieve for measuring the content of available heavy metals Cd, Cu, Ni, Pb, and Zn in the samples.

[0050] (2) Measuring the content of available heavy metals Cd, Cu, Ni, Pb, and Zn in the samples. The available heavy metals in the soil samples were measured with reference to "Determination of 8 available elements in soil - Diethylenetriaminepentaacetic acid extraction - Inductively coupled plasma optical emission spectrometry" (HJ804 - 2016). Each available element in the soil was extracted with a diethylenetriaminepentaacetic acid - calcium chloride - triethanolamine (DTPA-CaCl2-TEA) buffer solution, and the content of DTPA-Cd, DTPA-Cu, DTPA-Ni, DTPA-Pb, and DTPA-Zn in the extract was measured by ICP-MS. The results are as Figure 1 shown.

[0051] According to Figure 1As can be seen from (a) to (e), compared with the blank soil sample, the addition of sludge - bagasse - calcium oxide biochar effectively reduced the content of available heavy metals in the soil. Compared with the blank control, after adding 2%, 4%, and 6% of sludge - bagasse - calcium oxide biochar, the DTPA - Cd concentrations in the soil samples decreased by 46.19%, 61.09%, and 58.19% respectively, the DTPA - Cu concentrations decreased by 46.87%, 61.67%, and 61.50% respectively, the DTPA - Ni concentrations decreased by 56.54%, 62.50%, and 69.82% respectively, the DTPA - Pb concentrations decreased by 15.75%, 34.19%, and 29.64% respectively, and the DTPA - Zn concentration decreased by 42.01%, 56.80%, and 52.85% respectively. Given the high toxicity index of Cd, its significant impact on environmental risk is obvious, and it is significantly reduced compared with the blank control, indicating that sludge - bagasse - calcium oxide biochar has an effective passivation effect on heavy metals in the soil.

[0052] Application Example 2

[0053] A method and application for improving the physical and chemical properties of heavy metal - contaminated soil by using the co - pyrolysis biochar of sludge, bagasse, and calcium oxide as a soil additive. The co - pyrolysis biochar of sludge, bagasse, and calcium oxide is applied to heavy metal - contaminated soil to study its effects on the physical and chemical properties of heavy metal - contaminated soil, such as pH value, electrical conductivity (EC), and cation exchange capacity (CEC). The method is as follows:

[0054] (1) Soil experiment: The sludge, bagasse, and calcium oxide biochar prepared in Example 1 were applied to heavy metal - contaminated soil. The heavy metal - contaminated soil used in the experiment was taken from the hydrometallurgical copper base in Yuxi City, Yunnan Province, China. It was air - dried at room temperature and passed through a 20 - mesh sieve for standby. The sludge - bagasse - calcium oxide biochar was added to the heavy metal - contaminated soil samples at 2%, 4%, and 6% of the total sample mass ratio. The sample without adding sludge - bagasse - calcium oxide was the heavy metal - contaminated soil blank control group. After the samples were mixed evenly, they were transferred to flowerpots. There was gauze and filter paper at the bottom of the flowerpots to prevent soil loss. During the experiment, the soil moisture content was maintained at 70% of the field water - holding capacity. The entire experimental period lasted for 49 days. Samples were collected from each flowerpot at 0, 7, 14, 21, 28, 35, 42, and 49 d, air - dried, and passed through a 20 - mesh sieve for measuring the pH value, electrical conductivity (EC), and cation exchange capacity (CEC) of the heavy metal - contaminated soil physical and chemical properties. The properties of the heavy metal - contaminated soil after adding the co - pyrolysis biochar of sludge, bagasse, and calcium oxide were studied.

[0055] (2) The pH, EC value of the soil samples were measured using a pH meter, a conductivity meter, and a portable oxidation-reduction potential meter respectively. The cation exchange capacity (CEC) was determined with reference to "Determination of soil cation exchange capacity - Extraction with hexaamminecobalt(III) chloride - Spectrophotometry" (HJ 889-2017). The results are as Figure 2 shown.

[0056] According to Figure 2 it can be seen that the application of sludge - bagasse - calcium oxide biochar caused the soil to turn from acidic to neutral and alkaline at the end of the incubation period. The EC value decreased by 13.80% - 50.11%, and the CEC value increased by 60.08% - 72.62%. Generally speaking, sludge - bagasse - calcium oxide biochar can significantly improve the physical and chemical properties of the soil by increasing the pH value, reducing the soil salinization degree, and increasing the CEC, highlighting the potential of sludge - bagasse - calcium oxide biochar as an effective soil conditioner in soil remediation.

[0057] Application Example 3

[0058] A method and application for improving the fertility characteristics of heavy metal - contaminated soil by using the co - pyrolysis biochar of sludge, bagasse, and calcium oxide as a soil additive. The co - pyrolysis biochar of sludge, bagasse, and calcium oxide was applied to heavy metal - contaminated soil to study its effects on the contents of organic matter (OM), total nitrogen (TN), available potassium (AK), and available phosphorus (AP) in the fertility characteristics of heavy metal - contaminated soil. The method is as follows:

[0059] (1) Soil experiment: The sludge, bagasse, and calcium oxide biochar prepared in Example 1 were applied to heavy metal - contaminated soil. The heavy metal - contaminated soil used in the experiment was taken from a copper hydrometallurgy base in Yuxi City, Yunnan Province, China. It was air - dried at room temperature and passed through a 20 - mesh sieve for standby. The sludge - bagasse - calcium oxide biochar was added to the heavy metal - contaminated soil samples at ratios of 2%, 4%, and 6% of the total sample mass. The sample without adding sludge - bagasse - calcium oxide was used as the heavy metal - contaminated soil blank control group. After the samples were mixed evenly, they were transferred into flower pots. A gauze and filter paper were laid at the bottom of the flower pots to prevent soil loss. During the experiment, the soil moisture content was maintained at 70% of the field capacity. The entire experimental period lasted for 49 days. Samples were collected from each flower pot at 0, 7, 14, 21, 28, 35, 42, and 49 d, air - dried, and passed through a 20 - mesh sieve for measuring the contents of organic matter (OM), total nitrogen (TN), available potassium (AK), and available phosphorus (AP) in the fertility characteristics of the heavy metal - contaminated soil, and to study the properties of the heavy metal - contaminated soil after adding the co - pyrolysis biochar of sludge, bagasse, and calcium oxide.

[0060] (2) The content of organic matter (OM) was determined using a fully automatic organic matter analyzer with reference to "Soil Testing - Part 6: Determination of Soil Organic Carbon and Organic Matter" (NY / T 1121.6 - 2006). The content of total nitrogen (TN) was determined using a fully automatic Kjeldahl nitrogen analyzer with reference to (NY / T 1121.24 - 2012). The content of available potassium (AK) was determined using ICP - OES with reference to "Available and Slowly Available Potassium in Soils" (NY / T 889 - 2004). The content of available phosphorus (AP) was determined using an ultraviolet - visible spectrophotometer with reference to "Soil Testing - Part 7: Determination of Available Phosphorus in Soils" (NY / T 1121.7 - 2014). The results are as Figure 3 shown.

[0061] According to Figure 3 it can be seen that after the end of the cultivation cycle, OM, TN, AK, and AP in the soil were all significantly improved. The content of OM increased from 8.74 to 27.10 g / kg, the content of TN increased from 0.364 to 0.583 g / kg, the content of AK increased from 45.00 to 109.00 mg / kg, and the content of AP increased from 5.60 to 113.00 mg / kg. The application of sludge - bagasse - calcium oxide biochar significantly improved the soil fertility characteristics, highlighting the potential of sludge - bagasse - calcium oxide biochar as a sustainable soil amendment and providing a promising solution for sustainable agriculture and environmental remediation.

[0062] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of sludge, bagasse, and calcium oxide co-pyrolyzed biochar as a soil additive, characterized in that: It includes the following steps: (1) Dry and grind the sludge and bagasse, then screen them, and then mix them with calcium oxide to obtain a mixture; (2) Pyrolyze the mixture obtained in step (1) under a nitrogen atmosphere, screen it after cooling to obtain sludge-bagasse-calcium oxide biochar.

2. The preparation method of the co-pyrolysis biochar of sludge, bagasse and calcium oxide as a soil additive according to claim 1, characterized in that: In step (1), the sludge and bagasse are mixed at a mass ratio of 1:

1. After drying and grinding, the sludge and bagasse pass through a 60-mesh sieve and a 20-mesh sieve respectively, and the addition amount of calcium oxide is 30% of the total mass of the mixture.

3. The preparation method of the sludge, bagasse, and calcium oxide co-pyrolysis biochar as a soil additive according to claim 1, characterized in that: In step (2), the temperature of the pyrolysis is 600 - 750 °C, the time of the pyrolysis is 1 - 2 h, and a biochar sample is obtained after cooling.

4. The co-pyrolysis biochar of sludge, bagasse and calcium oxide prepared by the method according to any one of claims 1 - 3.

5. The application of the co-pyrolysis biochar of sludge, bagasse and calcium oxide according to claim 4 in the remediation of heavy metal contaminated soil.

6. The application of the co-pyrolysis biochar of sludge, bagasse and calcium oxide in the remediation of heavy metal contaminated soil according to claim 5, characterized in that: The heavy metal contaminated soil without adding the co-pyrolysis biochar of sludge-bagasse-calcium oxide is used as a blank control group, and the addition amount of the sludge-bagasse-calcium oxide biochar is 2% - 6% of the total mass of the soil sample.

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