Introduction

The annual production of domestic waste continues to increase, and sanitary landfill remains an important disposal method for domestic waste1. However, due to the post-management mode and disposal technology, pollutants such as wastewater and leachate from waste have various degrees of leakage and intrusion into the soil during the waste stacking or after landfill closure, forming domestic-sources-contaminated soil2,3. The organic acid in the contaminated soil dissolves the alkaline cement because it contains a large amount of easily degradable organic matter, including sugars, organic acids, alcohols, and esters. In addition, greenhouse gases such as CH4 and CO2 will be released as organic matter degrades. The generated gases accumulate and expand locally within the soil, destroying the soil structure, resulting in environmental engineering geological issues such as the decrease in the strength of the contaminated soil and the release of a large amount of greenhouse gases4,5. Therefore, the synergistic remediation of the reinforcement and carbon sequestration of domestic-sources-contaminated soils has become an important practical need.

Biochar is a recalcitrant, stable, and highly aromatic solid material generated from biomass through high - temperature pyrolysis under anoxic or oxygen—limited conditions6, which is widely used in soil carbon sequestration and contaminated soil remediation7,8,9,10. It has extremely high boiling point, and strong resistance to physical, chemical, and biological decomposition, making it stable in natural soil conditions for thousands of years and having a strong capacity for soil carbon sequestration11. Additionally, the strong adsorption capacity of biochar enables it to adsorb and fix organic matter in the soil, slowing down or even inhibiting greenhouse gas emissions12,13. Currently, research on biochar-mediated soil carbon sequestration focused on farmland soil, with an emphasis on carbon sequestration and promoting plant growth14. However, there are few studies on the carbon sequestration effect of biochar on the migration and transformation of soil organic matter. Due to the strong adsorption of biochar, it can adsorb and fix organic pollutants and heavy metal pollutants in the soil to achieve environmental management of contaminated soil15. Regarding the research on biochar in soil engineering management, although the current research on biochar for soil reinforce is limited, it has been found that biochar can improve soil strength16. By adsorbing organic materials, biochar can cement soil particles together and create a stable aggregate structure17. Moreover, because biochar is alkaline, it can neutralize H+ in the soil, preventing the corrosion damage of the soil structure by acidic substances and creating a suitable formation environment for carbonate precipitation18,19. In addition, due to the strong capillary action of biochar, pore water is transported from areas of the soil to areas of the biochar20. This causes the lubricated soil particle surface to become rough and exposed contact surfaces, while also increasing the capillary force of soil and the precipitation of solutes in the pore water, enhancing the cementing effect on soil particles21.

Although previous studies have shown that biochar has potential advantages in the remediation of domestic-sources-contaminated soil and the control of organic pollutants, however, there is currently no research on the collaborative remediation of biochar for the engineering treatment (reinforcement) of domestic-source polluted soil and environmental treatment (including two aspects: fixing pollutants and inhibiting the degradation of organic pollutants to sequester carbon). To enable the environmental and engineering co-remediation of biochar in domestic-sources-contaminated soil, it is essential to investigate the coupling law between the migration and transformation of organic matter in the soil and the response characteristics of engineering properties of the soil under the action of biochar. Therefore, this paper takes domestic-sources-contaminated soil and bamboo biochar as the research objects. The effects of biochar on the strength, deformation, permeability and organic pollutant loss in the leaching process of domestic-sources-contaminated soil were characterized and analyzed through laboratory simulation and remolding of the domestic-sources-contaminated soil remediated by biochar with different dosage and particle size, combined with geotechnical experiments and thermal gravimetric analysis. The environmental remediation effect and engineering remediation effect of biochar on domestic-sources-contaminated soil were evaluated. It should be particularly noted that the environmental remediation effect involved in this study focuses on the fixation effect of biochar on organic pollutants. Furthermore, the remediation mechanism of biochar on domestic-sources-contaminated soil was revealed based on the key characteristics of biochar.

Materials and methods

Domestic-sources-contaminated soil

The domestic-sources-contaminated soil used in the experiments was collected from an abandoned informal landfill in Xuzhou City, Jiangsu Province. Both undisturbed and disturbed samples of domestic-sources-contaminated soil, as well as undisturbed samples of uncontaminated soil near the landfill, were obtained through trench excavation (Fig. 1). The collected soil was sealed and refrigerated at 4 °C to inhibit the rapid oxidation and degradation of organic matter in the samples before being returned to the laboratory. The sample preparation was completed on the day of collection, and the soil samples were cured and tested within 15 days.

Fig. 1
figure 1

Location of sampling for domestic-sources-contaminated soil (The digital drawings were created by Y.L. Guo using Microsoft Office PowerPoint 2019 https://products.office.com/.)

Indoor geotechnical experiments were conducted to analyze the basic properties of the undisturbed domestic-sources-contaminated soil and uncontaminated soil, as shown in Table 1. Each sample is tested synchronously three times, and the average value is taken as the final result. When the deviations among the three test results are relatively large, the test should be carried out again until the standard error of the test is less than 0.5. The comparative test results revealed that the domestic-sources-contaminated soil has a higher organic matter content and a larger proportion of fine-grained particles compared to the uncontaminated soil, and exhibits a lower shear strength. The comparison results further illustrate that there is a problem of strength weakening in the domestic-source polluted soil.

Table 1 Basic properties of domestic-sources-contaminated soil and uncontaminated soil.
Fig. 2
figure 2

Bamboo biochar with different particle sizes (The digital drawings were created by Y.L. Guo using Microsoft Office PowerPoint 2019 https://products.office.com/.)

Biochar

Bamboo biochar with higher particle hardness was selected as the subject of the experimental study. The higher the pyrolysis temperature and the longer the carbonization time, the more developed the pores of the biochar, the stronger the alkalinity, and the more stable the properties22. Therefore, the preparation conditions of bamboo biochar are pyrolysis at a temperature of 700 °C for 4 h in an anaerobic environment. Figure 2 shows the bamboo biochar of different particle sizes prepared.

Testing methods

In order to control the variables and simulate the actual working conditions of biochar-remediated domestic-sources-contaminated soil as closely as possible, a constant pressure layered compaction method was used to prepare biochar-remediated domestic-sources-contaminated soil samples, with a compaction pressure of 250 kPa. The samples were sealed and allowed to cure for seven days at 20 °C in a temperature-controlled environment to bring the biochar and contaminated soil system into equilibrium. Two parts of simulation experiments were conducted sequentially to explore the remediation effects of biochar dosage and particle size on domestic-sources-contaminated soil: (a) Six biochar dosages of 0%, 3%, 6%, 9%, 12%, and 15% (the ratio of biochar mass to dry soil mass), with a biochar particle size of 1–3 mm. (b) Four different biochar particle sizes of less than 0.5 mm, 0.5–1 mm, 1–3 mm, and 3–5 mm, with a biochar dosage set at 6%.

The permeability coefficient of the soil and the loss of organic matter in the soil under leaching were used as evaluation indicators for the degree of organic matter fixation by biochar in domestic-sources-contaminated soil. (a) Test of soil permeability coefficient: According to the relevant standards of “Specification of Soil Test” (GB / T50124-2019), the self-built air pressure controlled constant head soil permeability test apparatus (Fig. 3) was used to carry out the constant head Darcy experiment on the domestic-sources-contaminated soil remediated by biochar. A stable air pressure of 150 kPa was provided by an air pressure controller to control the seepage pressure, and the final stable permeability coefficient of the soil was measured. (b) Test of the loss of organic matter in the soil under leaching: According to the relevant standards of “Test Methods of Soils for Highway Engineering” (GB / T50124-2019) for measuring the content of organic matter in soil by the combustion method, the organic matter content in the domestic-sources-contaminated soil before and after 10 h of leaching was tested by thermogravimetric analysis. The specific experimental temperature rise scheme is shown in Fig. 3, which first raises the temperature to 65 °C at a rate of 20 °C/min, maintains 65 °C for 1 h to evaporate the free water in the soil, and then raises the temperature to 950 °C at a rate of 20 °C/min, and maintains 950 °C for 0.5 h to evaporate the organic matter in the soil.

The shear strength indexes of saturated soil and the compression coefficient of saturated soil were used as evaluation indicators for the impact of biochar on the mechanical properties of domestic-sources-contaminated soil. Referring to the relevant standards of “Specification of Soil Test” (GB/T50124-2019), the biochar-remediated domestic-sources-contaminated soil was first vacuum saturated using a vacuum saturation apparatus, and then the shear strength index and compression coefficient of the soil were tested by triaxial shear test and consolidation test, respectively.

Fig. 3
figure 3

Seepage leaching test apparatus and heating scheme of thermogravimetric analysis (The digital drawings were created by Y.L. Guo using Microsoft Office PowerPoint 2019 https://products.office.com/ and Origin 2018 https://www.originlab.com.)

During the experimental testing, three parallel experiments were set up. When the standard error of the experiments is less than 0.5, the average value is taken as the final result. When the deviations among the results of the three tests are relatively large, the tests should be carried out again until the standard error is less than 0.5.

Results

The impact of biochar on the permeability and organic matter migration of domestic-sources-contaminated soil

Figure 4a, c illustrates the variation of the permeability coefficient of domestic-sources-contaminated soil under different biochar dosages and particle sizes. The overall trend of the permeability coefficient for domestic-sources-contaminated soil was that it gradually increased with the increase of biochar dosage and particle size, and there was a turning mutation point. When the biochar dosage was less than 12% and the particle size was below 1–3 mm, the impact of biochar on the permeability coefficient of domestic-sources-contaminated soil was small, and the permeability coefficient of the soil was relatively low. When the biochar dosage exceeded 12% and the particle size was above 1–3 mm, the permeability coefficient of the domestic-sources-contaminated soil increased sharply with the increase of biochar dosage and the enlargement of particle size. Due to its porous nature and strong adsorption capacity, biochar adsorbs pore water when the dosage was less than 12% and the particle size was within 1–3 mm. This increased the seepage resistance of pore water in the domestic-sources-contaminated soil. When the biochar dosage was greater than 12% and the particle size was above 1–3 mm, the addition of biochar to the domestic-sources-contaminated soil increases the porosity of the soil by creating channels for the seepage of pore water.

Fig. 4
figure 4

Variation of the permeability coefficient or organic matter loss of domestic-sources-contaminated soil under different biochar dosages and particle sizes (The digital drawings were created by Y.L. Guo using Origin 2018 https://www.originlab.com.)

Figure 4b, d shows the variation of the organic matter loss of domestic-sources-contaminated soil per unit volume of water flow or per unit time of leaching under different biochar dosages and particle sizes. Comparing Fig. 4, it can be see that the domestic-sources-contaminated soil had a relatively small permeability coefficient when the biochar dosage was less than 12% and the particle size was less than 1–3 mm, the organic matter loss of the domestic-sources-contaminated soil per unit volume of water flow gradually decreased as the biochar dosage and particle size increased, indicating that biochar had the ability to adsorb and fix organic contaminants in the soil. When the biochar dosage was greater than 12% and the particle size was larger than 1–3 mm, the organic matter loss of the soil per unit volume of water flow stabilized. However, for the organic matter loss per unit time of leaching, at a biochar dosage of 12% and a particle size of 1–3 mm, the organic matter loss of the domestic sources contaminated soil was at its lowest. At a biochar dosage of 15% and a particle size of 3–5 mm, the organic matter loss per unit time of leaching was higher, because, despite the small organic matter loss per unit volume of water flow, the soil had a larger permeability coefficient, which increased the amount of water seeped through in a unit of time.

Fig. 5
figure 5

Variation of the shear strength indexes of domestic-sources-contaminated soil under different biochar dosages and particle sizes (The digital drawings were created by Y.L. Guo using Origin 2018 https://www.originlab.com.)

The impact of biochar on the mechanical properties of domestic-sources-contaminated soil

Figure 5 shows the variation of cohesion and internal friction angle of domestic-sources-contaminated soil under different biochar dosages and particle sizes. It is evident that both the cohesion and internal friction angle of the domestic-sources-contaminated soil first increased and then decreased with the increase of biochar dosage and particle size. The strong adsorption capacity of biochar mainly enhanced the bonding strength between biochar and soil particles in the domestic-sources-contaminated soil at low biochar dosages and small particle sizes. The main effect of biochar at high dosage and large particle size was to enlarge the pores in the domestic-sources-contaminated soil, causing the soil to become looser and lose strength. Therefore, it could be concluded that there is an effective threshold for the remediation effect of biochar dosage and particle size on domestic-sources-contaminated soil. Specifically, when the biochar dosage was between 3% and 12%, and the particle size was between < 0.5 mm and 3-5 mm, the strength of the domestic-sources-contaminated soil increased, and the remediation effect of biochar dosage on the domestic-sources-contaminated soil was stronger than that of particle size.

The impact of biochar on the deformation of domestic-sources-contaminated soil

Figure 6 illustrates the variation of the compression coefficient (at a pressure of 100-200 kPa) of domestic-sources-contaminated soil under different biochar dosages and particle sizes. According to the evaluation standard for soil compression coefficient (at a pressure of 100-200 kPa) in “Code for Design of Steel Structure of Railway Bridge” (TB10094-2017), the compressibility of the soil is divided into low, medium, and high based on the boundaries of 0.1MPa− 1 and 0.5MPa− 1. It can be observed that the compression coefficient of the domestic-sources-contaminated soil without biochar addition was relatively large, belonging to high compressibility soil. The addition of biochar can reduce the compression coefficient of the domestic-sources-contaminated soil, transforming it into medium compressibility soil. Consistent with the impact of biochar on the strength of the domestic-sources-contaminated soil, the compressibility first decreased and then increased with the increase of biochar dosage and particle size. When the biochar dosage was between 3% and 12%, and the particle size was between < 0.5 mm and 3-5 mm, the compressibility of the domestic-sources-contaminated soil was lower than that of the soil without biochar addition.

Fig. 6
figure 6

Variation of the compression coefficient of domestic-sources-contaminated soil under different biochar dosages and particle sizes (The digital drawings were created by Y.L. Guo using Origin 2018 https://www.originlab.com.)

Discussion

Analysis of the environmental remediation effectiveness of biochar on domestic-source contaminated soil

Stabilizing and fixing organic contaminants are critical measures for the environmental remediation effects of biochar on domestic-sources-contaminated soil. The effects of biochar are reflected in two respects. First, the adsorption strength of soil for organic contaminants was increased, indicating an enhanced degree of stabilization and fixation. Second, the permeability of the domestic-sources-contaminated soil was improved, indicating a reduced degree of stabilization and fixation. The results showed that a strong fixation effect occurred when the dosage and particle size of biochar increased. This resulted in a gradual decrease in the amount of organic matter lost in the soil per unit volume of water flow, reaching a stable state when the dosage exceeded 12% and the particle size was above 1–3 mm. When the biochar dosage was 15% and the particle size was 3–5 mm, the leachate loss of organic matter per unit volume was relatively low. Nevertheless, owing to the increased permeability coefficient of the soil, the overall water flow within the same time frame is higher, leading to a higher leaching loss of organic matter per unit time.

Therefore, according to the tests of permeability coefficient and the organic matter loss in the soil, the optimal environmental remediation effect was achieved when the biochar dosage was 12% and particle size was 1–3 mm. Specifically, at a biochar dosage of 12%, the organic matter loss in the soil per unit volume of water flow was 0.0449%/cm2, lower than that of unremedied soil (0.7411%/cm2), and the organic matter loss per unit time of leaching was 0.0370%/h, lower than that of unremedied soil (0.0920%/h). When the biochar particle size was 1–3 mm, the organic matter loss per unit volume of water flow was 0.1863%/cm2, lower than that of unremedied soil (0.7411%/cm2), and the organic matter loss per unit time of leaching was 0.0610%/h, lower than that of unremedied soil (0.0920%/h).

Analysis of the engineering remediation effectiveness of biochar on domestic-source contaminated soil

The engineering remediation effects of biochar on domestic-sources-contaminated soil are reflected in the increased strength and reduced compressibility of the soil after biochar remediation. The results show that as the biochar dosage and particle size increased, the cohesion, internal friction angle, and deformation resistance of the soil exhibited an initial increase followed by a decrease. Thus, according to the tests of mechanical properties, with cohesion, internal friction angle, and compression coefficient as evaluation indicators, the biochar dosage and particle size both exhibited significant effectiveness within their optimal application ranges in remediating the domestic-sources-contaminated soil.

Specifically, the optimal range for biochar dosage was 6–12%. The cohesion of the remediated soil ranged from 40.35 to 59.83 kPa, which was higher than that of the unremedied soil (21.15 kPa); the internal friction angle ranged from 2.26° to 3.87°, which was higher than that of the unremedied soil (0.42°); and the compression coefficient ranges from 0.340 MPa− 1 to 0.410 MPa− 1, which was lower than that of the unremedied soil (0.502 MPa− 1). The optimal range for biochar particle size was less than 0.5 mm to 3–5 mm.The cohesion of the remediated soil ranged from 35.07 kPa to 43.58 kPa, which was higher than that of the unremedied soil (21.15 kPa); the internal friction angle ranged from 1.07° to 2.80°, which was higher than that of the unremedied soil (0.42°); and the compression coefficient ranged from 0.260 MPa− 1 to 0.384 MPa− 1, which was lower than that of the unremedied soil (0.502 MPa− 1).

In summary, a comprehensively analysis of the tests, considering both the environmental and engineering remediation effects of biochar on domestic-sources-contaminated soil, revealed that the optimal comprehensive remediation effect was achieved when the biochar dosage was 12% and the particle size was 1–3 mm. Specifically, at this dosage, biochar reduced the organic matter loss in the soil per unit volume of water flow by 0.6963%/cm³ and the organic matter loss per unit time of leaching by 0.0550%/h. It also enhanced the mechanical properties of the remediated soil, increasing cohesion by 38.68 kPa, the internal friction angle by 3.45°, and decreasing the compression coefficient by 0.092 MPa− 1. For the particle size of 1–3 mm, biochar reduced the organic matter loss per unit volume of water flow by 0.5548%/cm2, the organic matter loss per unit time of leaching by 0.0310%/h. Meanwhile, it improved soil cohesion by 15.52 kPa, increased the internal friction angle by 2.38°, and reduced the compression coefficient by 0.134 MPa− 1.

Remediation mechanisms of biochar on domestic-sources-contaminated soil

In order to deeply reveal the mechanisms of biochar in the engineering remediation (reinforcement) and environmental remediation (fixation of pollutants) of domestic-source polluted soil, the properties of bamboo biochar were tested by SEM, XRF and FTIR to obtain the composition and structural characteristics of biochar. The test results are shown in Fig. 7. It can be found that the surface of the bamboo biochar used in the experiment contains a large number of original fibrous pores and pyrolysis carbonization pores. At the same time, it also contains a large amount of alkali metals such as K, Al, Ca, Mg, and oxygen-containing functional groups such as –OH and C–O.

These attributes biochar with a suite of desirable properties, such as carbon stability, high porosity, adsorption, acid-base buffering capabilities23. Based on the key characteristics of biochar, the remediation mechanism of biochar on domestic-sources-contaminated soil mainly includes adsorption and agglomeration, regulation of physicochemical properties, and alteration of structural (Fig. 8).

Fig. 7
figure 7

Morphology and composition characteristics of bamboo biochar (The digital drawings were created by Y.L. Guo using Microsoft Office PowerPoint 2019 https://products.office.com/ and Origin 2018 https://www.originlab.com.)

Fig. 8
figure 8

Schematic diagram of the mechanism of biochar in remediating domestic-source polluted soil (The digital drawings were created by Y.L. Guo using Microsoft Office PowerPoint 2019 https://products.office.com/.)

Adsorption and agglomeration: Biochar contains abundant pores and oxygen-containing functional groups that make it have a strong adsorption effect on organic contaminants and water molecules24. Biochar fixes organic contaminants in domestic-sources-contaminated soil inside and on the surface of biochar through physical adsorption and chemical adsorption, which can prevent the migration and transformation of organic contaminants in soil and realize the environmental remediation on domestic-sources-contaminated soil25,26. Organic contaminants adsorbed onto the biochar surface aggregated at the contact points with soil particles, facilitating the agglomeration and cementation of soil particles27. This process enhanced the mechanical strength of the soil and reduces its compressibility. Additionally, oxygen-rich functional groups on the biochar surface interacted with pore water molecules in domestic-sources-contaminated soil through hydrogen bonding, which augmented the capacity of soil to retain water28. This interaction increased the drag on seepage flow, manifesting macroscopically as a decreased permeability of the soil.

Regulation of physicochemical properties: The regulation of biochar on the physicochemical properties of domestic-sources-contaminated soil was primarily reflected in its modulation of the pH and the composition of pore water. The alkaline substance within biochar can neutralize organic acids in the soil29, preventing their corrosive effects on alkaline cementing materials. thereby maintaining soil strength and deformation resistance. This resulted in a macroscopic effect that helped to prevent the weakening of the strength and the resistance to deformation of the domestic-sources-contaminated soil. Furthermore, the presence of metal ions in biochar, when introduced to domestic-sources-contaminated soil, elevated the concentration of metal cations within the pore water30, thereby reducing the thickness of the double electric layer of the soil. This led to an enhanced strength and an improved capacity to resist deformation in the domestic-sources-contaminated soil.

Alteration of structural: Biochar is abundant in naturally occurring fibrous pores and pyrolytic carbonization pores31. The larger particles of biochar can form a supporting framework within the soil, increasing the its porosity and the quantity of interconnected pores. Macroscopically, this resulted in a decrease in the strength and compressibility resistance of the domestic-sources-contaminated soil, and an increase in its permeability, which weakened the fixation degree of organic contaminants.

The Interplay Between Engineering Remediation and Environmental Restoration.

According to the changes of engineering remediation evaluation indexes such as the strength, deformation and permeability of domestic-source polluted soil, as well as environmental remediation indexes such as the loss of organic matter in domestic-source polluted soil during the leaching process, with the variation of the particle size and dosage of biochar, it can be found that there is a significant synergistic effect between the reinforcement and pollution remediation of domestic-source polluted soil by biochar. Both show that the remediation effect first increases and then decreases with the increase of the dosage or particle size of biochar (Fig. 9).

Fig. 9
figure 9

Coupling relationship diagram between engineering restoration and environmental restoration (The digital drawings were created by Y.L. Guo using Microsoft Office PowerPoint 2019 https://products.office.com/.)

The key factor for this coupling effect is that after biochar is added to the soil, it will affect the soil structure and soil adsorption properties, thereby influencing the soil permeability and the fixation degree of organic matter. The addition of biochar mainly affects the permeability of domestic-source polluted soil by changing the soil structure and increasing soil pores. When the dosage of biochar is small or the particle size is small, it has little impact on the soil structure, and the soil permeability remains basically unchanged. However, when the dosage of biochar is large or the particle size is large, it has a significant impact on the soil structure, and the soil permeability increases. Regarding the influence of biochar addition on the fixation degree of organic matter in domestic-source polluted soil, the larger the dosage or particle size of biochar, the better the fixation degree of organic matter. However, when the permeability is high, due to the strong leaching intensity, the loss of organic matter increases. Therefore, on the premise of ensuring a small permeability coefficient, increasing the dosage or particle size of biochar as much as possible can achieve the optimal environmental treatment effect. For the optimal engineering and environmental collaborative treatment, it is necessary to meet the requirements of increasing the soil strength, reducing the compressibility, and enhancing the fixation degree of organic matter.

Therefore, in this study, the conditions for achieving efficient collaborative treatment of soil engineering and the environment are that the dosage of biochar is 12% and the particle size is 1–3 mm. When the dosage of biochar is less than 12% or the particle size is less than 1–3 mm, with the increase of the dosage or particle size of biochar, the permeability coefficient of the soil slowly increased and then suddenly increased. The shear strength increased initially but then decreased, and the compression coefficient followed the opposite pattern, decreasing before increasing. This was mainly because at lower dosages and smaller particle sizes, the effects of biochar on domestic-sources-contaminated soil were dominated by adsorption and aggregation and regulation of physicochemical properties, while at higher dosages and larger particle sizes, the alteration of structural became predominant.

Conclusion

In conclusion, biochar plays a notable role in the environmental remediation (adsorption and fixation of organic contaminants) and engineering remediation (reinforcement and enhancement of deformation resistance) of domestic-sources-contaminated soil. There existed an optimal range for both the dosage and particle size of biochar that significantly contributed to the remediation process, achieving a synergistic environmental and engineering remediation of the soil. Under the conditions of this experimental study, the best results for the synergistic environmental and engineering remediation of domestic-sources-contaminated soil by biochar were obtained with a biochar dosage of 12% and a particle size of 1–3 mm. The remediation mechanisms of biochar on domestic-sources-contaminated soil mainly included adsorption and agglomeration, regulation of physicochemical properties, and alteration of structural.

However, although this study preliminarily confirmed the feasibility of biochar in the synergistic environmental and engineering remediation of domestic-sources-contaminated soil, the experimental testing period was relatively short. Given the easily degradable nature of organic matter in domestic-sources-contaminated soil, further exploration is needed regarding the impact of biochar on the degradation process of organic contaminants and the dynamic response characteristics of the engineering properties of soil. Moreover, the aging effect of biochar on the remediation of domestic-sources-contaminated soil directly affects the long-term stability of biochar in the synergistic environmental and engineering remediation of such soil.