A gel slow-release remediation material for organic contaminated soil and a preparation method thereof

Abstract

The present application belongs to the technical field of contaminated soil remediation, and relates to a gel slow-release remediation material for organic contaminated soil and a preparation method thereof, which comprises the following steps: inoculating high-efficiency petroleum hydrocarbon-degrading bacteria into LB liquid culture medium and oscillating culture, centrifuging and resuspending to obtain a bacterial suspension; dispersing attapulgite powder in the bacterial suspension to obtain a compound; uniformly mixing the compound with a sodium alginate solution to obtain a core slurry; dropping the core slurry into a calcium chloride solution through a syringe to obtain a core microsphere; uniformly mixing potassium persulfate, calcium lactate and deionized water to obtain a cross-linking solution; soaking the core microsphere in the pre-cooled cross-linking solution, and cross-linking under light-proof conditions to obtain an intermediate microsphere; uniformly mixing sodium alginate, sodium lactate, sodium bicarbonate, a surfactant and deionized water to obtain a coating solution; soaking the intermediate microsphere in the coating solution, filtering out, and then soaking in a calcium chloride solution again, and cross-linking by standing.

Description

Technical Field

[0001] This invention belongs to the field of contaminated soil remediation technology, and relates to a gel slow-release remediation material for organically contaminated soil and its preparation method. Background Technology

[0002] Pollutants such as petroleum hydrocarbons, polycyclic aromatic hydrocarbons, pesticides, and organochlorine compounds have posed a threat to the sustainable use of land resources and the ecological security of agricultural products. Currently, remediation technologies for organically contaminated soils mainly fall into three categories: physical, chemical, and biological. Physical methods, such as soil replacement and thermal treatment, are effective quickly but are costly and can easily damage soil structure; chemical methods, such as chemical oxidation-reduction and soil leaching, may cause secondary pollution; while bioremediation technologies are environmentally friendly, their remediation cycles are long and their efficiency is limited by factors such as climate, geographical conditions, and the form in which pollutants exist. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a gel-based slow-release remediation material for organically contaminated soil and its preparation method. Traditional single chemical oxidation cannot completely mineralize organic pollutants and produces intermediate products; while biodegradation has low efficiency in treating organic pollutants. The present invention combines chemical oxidation and biodegradation, achieving complementary advantages of the two treatment methods.

[0004] To achieve this objective, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a method for preparing a gel-release remediation material for organically contaminated soil, the preparation method comprising:

[0006] (I) The highly efficient petroleum hydrocarbon degrading bacteria were inoculated into LB liquid medium and cultured by shaking. After centrifugation and resuspension, a bacterial suspension was obtained. Attapulgite powder was dispersed in the bacterial suspension, and the mixture was shaken to adsorb and centrifuged to obtain a complex. The complex was mixed evenly with sodium alginate solution to obtain a core slurry. The core slurry was dropped into calcium chloride solution through a syringe and gelled to obtain core microspheres.

[0007] (II) Potassium persulfate, calcium lactate and deionized water are mixed evenly to obtain a crosslinking solution; the core microspheres are immersed in the pre-cooled crosslinking solution, and crosslinked under light-protected conditions. The mixture is then filtered out and washed to obtain the intermediate microspheres.

[0008] (III) Sodium alginate, sodium lactate, sodium bicarbonate, surfactant and deionized water are mixed evenly to obtain a coating solution; the intermediate microspheres are immersed in the coating solution, filtered out and then immersed in calcium chloride solution, allowed to stand for crosslinking, then filtered out, washed, allowed to stand for curing and dried to obtain the gel sustained-release repair material.

[0009] This invention first uses calcium chloride for primary cross-linking to form a core microsphere containing highly efficient petroleum hydrocarbon-degrading bacteria, with attapulgite powder as a carrier. Then, calcium lactate is used for secondary cross-linking to form an intermediate layer encapsulating potassium persulfate on the surface of the core microspheres. Finally, calcium chloride is used for tertiary cross-linking to form a gel shell containing sodium lactate, sodium bicarbonate, and surfactants. During the remediation process, the gel shell first contacts the soil environment. The surfactants in the gel solubilize pollutants, and the dissolution of sodium bicarbonate creates a slightly alkaline environment in the surrounding soil, triggering the potassium persulfate treatment. Sodium lactate provides the carbon source needed for microbial growth and reproduction. Subsequently, the potassium persulfate in the intermediate layer slowly diffuses, generating free radicals in the slightly alkaline environment, chemically oxidizing the pollutants and converting them into easily biodegradable small-molecule intermediates. Finally, the highly efficient petroleum hydrocarbon-degrading bacteria loaded in the core microspheres are activated and released, spreading and colonizing in the soil, mineralizing the intermediates adsorbed and enriched by the attapulgite. Chemical oxidation alone cannot completely mineralize organic pollutants and will produce intermediate products; while biodegradation alone has low efficiency in treating organic pollutants. This invention combines chemical oxidation and biodegradation, achieving the complementary advantages of the two treatment processes.

[0010] In the preparation process, this invention first prepares microspheres with a core of highly efficient petroleum hydrocarbon-degrading bacteria loaded with attapulgite clay. The core slurry loaded with the degrading bacteria and attapulgite clay is dropped into a calcium chloride solution, and gel solidifies to form the core microspheres. This gel solidification securely embeds the bacteria and attapulgite clay within the core microspheres, providing physical protection and preventing bacterial loss. Furthermore, the resulting gel network has a certain porosity, ensuring the gas and nutrient exchange necessary for the survival of the internal bacteria. Simultaneously, a large number of unreacted free carboxyl groups remain inside and on the surface of the gel, providing numerous carboxyl reaction sites for subsequent secondary crosslinking with calcium lactate.

[0011] Subsequently, the formed core microspheres were immersed in a crosslinking solution containing calcium lactate and potassium persulfate. Calcium ions in the solution react with free carboxyl groups on the surface of the core microspheres in a secondary crosslinking reaction, forming a new gel layer with a higher degree of crosslinking and a denser network on the surface of the core microspheres. Simultaneously, potassium persulfate dissolved in the crosslinking solution enters the newly formed gel network during the secondary crosslinking process, ultimately yielding an intermediate layer loaded with potassium persulfate. Calcium lactate was used instead of calcium chloride during the secondary crosslinking process to avoid the redox reaction between chloride ions and potassium persulfate, thus ensuring the stability of the potassium persulfate.

[0012] Finally, the microspheres loaded with potassium persulfate intermediate layer were immersed in a coating solution containing sodium alginate, sodium lactate, sodium bicarbonate and surfactant, so that a layer of coating solution was adsorbed on the surface. Then, they were transferred to calcium chloride solution for a third cross-linking. The third cross-linking formed the outermost gel shell.

[0013] During application, the gel shell is the first component to function. When the material is applied to contaminated soil, the gel shell is the first to come into contact with the moisture in the soil environment. The surfactants contained within are rapidly released, solubilizing hydrophobic organic pollutants and improving their bioavailability. Simultaneously, the sodium bicarbonate in the gel shell slowly dissolves, creating a mildly alkaline environment in the surrounding soil. This alkaline environment activates the potassium persulfate in the intermediate layer, triggering the production of sulfate free radicals. The sodium lactate in the gel shell serves as a carbon source, providing nutrients to the highly efficient petroleum hydrocarbon-degrading bacteria loaded in the core microspheres and to soil microorganisms, stimulating microbial community proliferation.

[0014] The intermediate layer containing potassium persulfate then comes into play. This layer primarily controls the release of potassium persulfate while isolating it from the highly efficient petroleum hydrocarbon-degrading bacteria within the core microspheres, as well as from the sodium bicarbonate in the gel shell. As sodium bicarbonate is released from the gel shell, the soil environment surrounding the remediation material becomes slightly alkaline. The potassium persulfate, encapsulated in the dense gel network, is activated by this alkaline environment, generating sulfate free radicals. Because the potassium persulfate is fixed in the independent intermediate layer, its dissolution and activation processes are controlled by gel diffusion, preventing a sudden burst release and achieving sustained, slow oxidation. This process continuously oxidizes and decomposes recalcitrant macromolecular organic pollutants in the soil, transforming them into smaller, more hydrophilic organic acids, alcohols, and other intermediate products. This chemical oxidation significantly improves the biodegradability of organic pollutants, laying the foundation for the subsequent biomineralization by highly efficient petroleum hydrocarbon-degrading bacteria.

[0015] Finally, the core microspheres play a crucial role. Using attapulgite as a carrier, the core microspheres exert a dual function through their enormous specific surface area and adsorption capacity: on the one hand, they can efficiently immobilize and protect the degrading bacteria during the preparation stage, preventing bacterial inactivation in harsh soil environments; on the other hand, during soil remediation, organic pollutants are oxidized by potassium sulfate to form easily biodegradable intermediate products. Attapulgite can strongly adsorb these intermediate products, and the degrading bacteria loaded in the core can mineralize the intermediate products enriched in the attapulgite, converting them into carbon dioxide and water, thus achieving the complete removal of organic pollutants.

[0016] As a preferred technical solution of the present invention, in step (I), the temperature of the oscillation culture is 28~32℃, for example, it can be 28℃, 28.5℃, 29℃, 29.5℃, 30℃, 30.5℃, 31℃, 31.5℃ or 32℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] In some optional instances, the rotation speed of the oscillation culture is 150 to 200 rpm, for example, 150 rpm, 155 rpm, 160 rpm, 165 rpm, 170 rpm, 175 rpm, 180 rpm, 185 rpm, 190 rpm, 195 rpm or 200 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] In some optional instances, the oscillatory culture is carried out to the late logarithmic growth stage.

[0019] In some alternative instances, the centrifugation temperature is 3 to 5°C, for example, 3.0°C, 3.2°C, 3.4°C, 3.6°C, 3.8°C, 4.0°C, 4.2°C, 4.4°C, 4.6°C, 4.8°C, or 5.0°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0020] In some optional instances, the centrifugation speed is 7000~8000 rpm, for example, it can be 7000 rpm, 7100 rpm, 7200 rpm, 7300 rpm, 7400 rpm, 7500 rpm, 7600 rpm, 7700 rpm, 7800 rpm, 7900 rpm or 8000 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] As a preferred technical solution of the present invention, in step (I), the resuspension process includes:

[0022] Collect the centrifuged bacterial cells, add them to sterile physiological saline, disperse them evenly, centrifuge again, collect the centrifuged bacterial cells, add them to physiological saline, and prepare the bacterial suspension.

[0023] In some optional instances, the concentration of the bacterial suspension is 1 × 10⁻⁶. 9 ~5×10 9 CFU / mL, for example, could be 1×10⁻⁶ 9 CFU / mL, 1.5×10 9 CFU / mL, 2×10 9 CFU / mL, 2.5×10 9 CFU / mL, 3×10 9 CFU / mL, 3.5×10 9 CFU / mL, 4×10 9 CFU / mL, 4.5×10 9 CFU / mL or 5×10 9 The value is CFU / mL, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0024] As a preferred technical solution of the present invention, in step (I), the attapulgite clay is dried at 100~110℃ for 2 hours, and then crushed through a 200-mesh sieve to obtain the attapulgite clay powder.

[0025] In some alternative examples, the solid-liquid ratio of the attapulgite powder to the bacterial suspension is 1 g:(1~2) mL, for example, it can be 1 g:1.0 mL, 1 g:1.1 mL, 1 g:1.2 mL, 1 g:1.3 mL, 1 g:1.4 mL, 1 g:1.5 mL, 1 g:1.6 mL, 1 g:1.7 mL, 1 g:1.8 mL, 1 g:1.9 mL or 1 g:2.0 mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] The preferred efficient petroleum hydrocarbon degrading bacteria used in this invention are Pseudomonas malodorans strain KT2440, with the aim of achieving complete mineralization of pollutants.

[0027] In some optional instances, the rotational speed of the oscillating adsorption is 80 to 100 rpm, for example, 80 rpm, 82 rpm, 84 rpm, 86 rpm, 88 rpm, 90 rpm, 92 rpm, 94 rpm, 96 rpm, 98 rpm or 100 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] In some optional instances, the oscillatory adsorption time is 1 to 2 hours, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some alternative instances, the centrifugation temperature is 3 to 5°C, for example, 3.0°C, 3.2°C, 3.4°C, 3.6°C, 3.8°C, 4.0°C, 4.2°C, 4.4°C, 4.6°C, 4.8°C, or 5.0°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0030] In some optional instances, the centrifugation speed is 4000 to 5000 rpm, for example, 4000 rpm, 4100 rpm, 4200 rpm, 4300 rpm, 4400 rpm, 4500 rpm, 4600 rpm, 4700 rpm, 4800 rpm, 4900 rpm or 5000 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] In some optional instances, the centrifugation time is 4 to 6 minutes, for example, 4.0 minutes, 4.2 minutes, 4.4 minutes, 4.6 minutes, 4.8 minutes, 5.0 minutes, 5.2 minutes, 5.4 minutes, 5.6 minutes, 5.8 minutes, or 6.0 minutes, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0032] As a preferred technical solution of the present invention, in step (I), the mass fraction of the sodium alginate solution is 1.5~2.5wt%, for example, it can be 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, or 2.5wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In some alternative examples, the solid-liquid ratio of the complex to the sodium alginate solution is 1 g:(2.5~3.5) mL, for example, it can be 1 g:2.5 mL, 1 g:2.6 mL, 1 g:2.7 mL, 1 g:2.8 mL, 1 g:2.9 mL, 1 g:3.0 mL, 1 g:3.1 mL, 1 g:3.2 mL, 1 g:3.3 mL, 1 g:3.4 mL or 1 g:3.5 mL, but is not limited to the values ​​listed, other unlisted values ​​within this range are also applicable.

[0034] In some alternative instances, the inner diameter of the syringe needle is 1 to 1.2 mm, for example, it can be 1.0 mm, 1.02 mm, 1.04 mm, 1.06 mm, 1.08 mm, 1.1 mm, 1.12 mm, 1.14 mm, 1.16 mm, 1.18 mm or 1.2 mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] In some optional instances, the calcium chloride solution has a mass fraction of 2 to 3 wt%, for example, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0036] The core function of calcium chloride is to provide calcium ions, which react with the carboxyl groups on the sodium alginate molecular chain to form an ionic cross-linking reaction, causing the droplets to solidify instantly. This invention limits the mass fraction of the calcium chloride solution to 2-3 wt% to ensure sufficient diffusion of calcium ions into the microspheres, forming a core microsphere with high mechanical strength. If the concentration of the calcium chloride solution is too low, the gelation rate is too slow, resulting in a loose gel network structure with poor mechanical strength, making it prone to breakage and collapse. If the concentration of the calcium chloride solution is too high, an overly dense and hard outer shell will instantly form on the surface of the core microsphere, severely hindering the continued diffusion of external calcium ions into the interior of the core microsphere, ultimately forming a hard-outer-soft-inner structure, causing the core microsphere to crack due to uneven internal and external stress. Furthermore, the formation of a hard shell on the surface also reduces the number of carboxyl functional groups on the microsphere surface, affecting the subsequent secondary cross-linking of calcium lactate.

[0037] In some optional instances, the gel curing time is 15 to 25 minutes, for example, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes or 25 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] As a preferred technical solution of the present invention, in step (II), the mass fraction of potassium persulfate in the crosslinking solution is 5~6wt%, for example, it can be 5.0wt%, 5.1wt%, 5.2wt%, 5.3wt%, 5.4wt%, 5.5wt%, 5.6wt%, 5.7wt%, 5.8wt%, 5.9wt% or 6.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Potassium persulfate in the crosslinking solution acts as a chemical oxidation component. After the material is applied to the soil, the potassium persulfate is activated by sodium bicarbonate released from the gel shell, decomposing to produce sulfate free radicals with strong oxidizing properties. These sulfate free radicals can attack and destroy organic pollutants in the soil, oxidizing and decomposing large organic molecules into smaller molecule intermediates that are more easily utilized by microorganisms.

[0040] This invention limits the potassium persulfate concentration to 5-6 wt%, ensuring sufficient potassium persulfate loading for the material and guaranteeing its continuous and effective chemical oxidation capacity. When the potassium persulfate concentration is too low, its oxidation capacity for organic pollutants is insufficient, failing to fully oxidize and decompose them. Conversely, when the potassium persulfate concentration is too high, it leads to a rapid and excessive release of potassium persulfate, inhibiting microorganisms in the soil environment and the highly efficient petroleum hydrocarbon-degrading bacteria loaded in the core microspheres, thus affecting the biodegradation process.

[0041] In some optional examples, the mass fraction of calcium lactate in the crosslinking solution is 2 to 3 wt%, for example, it can be 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] When the core microspheres are immersed in a mixture containing calcium lactate and potassium persulfate, calcium ions in the solution diffuse into the interior of the core microspheres, undergoing a second ionic cross-linking reaction with unreacted free carboxyl groups in the gel network, thus forming a denser intermediate layer. Calcium lactate was chosen instead of calcium chloride because potassium persulfate is a strong oxidizing agent, while chloride ions in calcium chloride have some reducing properties. When the two come into contact in solution, a redox reaction occurs, which not only leads to premature consumption of potassium persulfate, reducing the chemical oxidation capacity of the final product, but also affects the secondary cross-linking. The lactate ions in calcium lactate are chemically stable and do not react with potassium persulfate, thus ensuring the stability of the potassium persulfate.

[0043] In some alternative instances, the crosslinking solution is precooled to 5-10°C, for example, 5.0°C, 5.5°C, 6.0°C, 6.5°C, 7.0°C, 7.5°C, 8.0°C, 8.5°C, 9.0°C, 9.5°C, or 10.0°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0044] In some optional instances, the static crosslinking time of the core microspheres in the crosslinking liquid is 25 to 35 minutes, for example, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes or 35 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0045] In some optional instances, the temperature at which the core microspheres are statically crosslinked in the crosslinking solution is 5 to 10°C, for example, 5.0°C, 5.5°C, 6.0°C, 6.5°C, 7.0°C, 7.5°C, 8.0°C, 8.5°C, 9.0°C, 9.5°C, or 10.0°C, for example, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0046] The crosslinking solution containing potassium persulfate and calcium lactate is pre-cooled to 5~10℃, and the temperature is also controlled at 5~10℃ during the crosslinking process. The reason is that potassium persulfate, as a strong oxidant, is prone to spontaneous decomposition and premature consumption at higher temperatures. The low-temperature environment prevents the thermal decomposition of potassium persulfate and ensures that it is stably embedded in the intermediate layer.

[0047] As a preferred technical solution of the present invention, in step (III), the mass fraction of sodium alginate in the coating solution is 2~3wt%, for example, it can be 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt% or 3.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] In some optional instances, the mass fraction of sodium lactate in the coating solution is 4 to 5 wt%, for example, it may be 4.0 wt%, 4.1 wt%, 4.2 wt%, 4.3 wt%, 4.4 wt%, 4.5 wt%, 4.6 wt%, 4.7 wt%, 4.8 wt%, 4.9 wt%, or 5.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0049] Sodium lactate in the gel shell acts as a biostimulant. When the material is applied to contaminated soil, as the gel shell swells and dissolves, sodium lactate is released into the surrounding soil environment, providing high-quality carbon and energy sources for the soil's own microorganisms and the degrading bacteria loaded in the core microspheres, stimulating the metabolism and reproduction of the microbial community.

[0050] In some optional instances, the mass fraction of sodium bicarbonate in the coating solution is 4 to 5 wt%, for example, it may be 4.0 wt%, 4.1 wt%, 4.2 wt%, 4.3 wt%, 4.4 wt%, 4.5 wt%, 4.6 wt%, 4.7 wt%, 4.8 wt%, 4.9 wt%, or 5.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] Sodium bicarbonate in the gel shell acts as a pH adjuster. When the material is applied to contaminated soil, sodium bicarbonate is slowly released as the gel shell dissolves, creating a mild and persistent alkaline environment around the material. Potassium persulfate decomposes under alkaline conditions, producing sulfate free radicals that chemically oxidize organic pollutants.

[0052] When the concentration of sodium bicarbonate is too low, the activation efficiency of potassium persulfate is too low, and potassium persulfate cannot generate sufficient sulfate free radicals. This results in insufficient chemical oxidation of organic pollutants, preventing some organic pollutants from being effectively converted into small-molecule intermediates and affecting the subsequent biodegradation effect of degrading bacteria. When the concentration of sodium bicarbonate is too high, it leads to excessively alkaline soil around the material, causing potassium persulfate to decompose rapidly and in large quantities, thus failing to exert a sustained and stable chemical oxidation effect.

[0053] In some optional instances, the surfactant in the coating solution has a mass fraction of 0.15 to 0.25 wt%, for example, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, 0.2 wt%, 0.21 wt%, 0.22 wt%, 0.23 wt%, 0.24 wt%, or 0.25 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0054] In some optional instances, the surfactant includes Tween-80.

[0055] In some optional instances, the immersion time of the intermediate microspheres in the coating solution is 15 to 20 minutes, for example, 15 minutes, 15.5 minutes, 16 minutes, 16.5 minutes, 17 minutes, 17.5 minutes, 18 minutes, 18.5 minutes, 19 minutes, 19.5 minutes, or 20 minutes, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0056] As a preferred technical solution of the present invention, in step (III), the mass fraction of the calcium chloride solution is 1.5~2wt%, for example, it can be 1.5wt%, 1.55wt%, 1.6wt%, 1.65wt%, 1.7wt%, 1.75wt%, 1.8wt%, 1.85wt%, 1.9wt%, 1.95wt%, or 2.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] In some optional instances, the time for the intermediate microspheres to stand and crosslink in the calcium chloride solution is 40 to 50 minutes, for example, 40 minutes, 41 minutes, 42 minutes, 43 minutes, 44 minutes, 45 minutes, 46 minutes, 47 minutes, 48 ​​minutes, 49 minutes or 50 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0058] In some alternative instances, the static curing temperature is 4 to 8°C, for example, 4.0°C, 4.5°C, 5.0°C, 5.5°C, 6.0°C, 6.5°C, 7.0°C, 7.5°C, or 8.0°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0059] In some optional instances, the settling time is 6 to 8 hours, for example, 6.0 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0060] In some alternative instances, the drying process involves air-drying the material at an environment of 28-30°C until the moisture content is 10-15%. For example, the ambient temperature can be 28°C, 28.2°C, 28.4°C, 28.6°C, 28.8°C, 29°C, 29.2°C, 29.4°C, 29.6°C, 29.8°C, or 30°C, and the moisture content can be 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, or 15%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0061] Secondly, the present invention provides a gel-release remediation material for organically contaminated soil prepared by the preparation method described in the first aspect.

[0062] As a preferred technical solution of the present invention, the gel sustained-release repair material includes a core microsphere, and an intermediate layer and a gel shell that are sequentially coated on the surface of the core microsphere from the inside out.

[0063] The core microspheres contain attapulgite powder and highly efficient petroleum hydrocarbon degrading bacteria loaded thereon, the intermediate layer contains potassium persulfate, and the gel shell contains sodium lactate, sodium bicarbonate, and surfactant.

[0064] The gel-release repair material prepared by this invention consists of a core microsphere, an intermediate layer, and a gel shell. Potassium persulfate is separately encapsulated in the intermediate layer of a dense gel network, sodium bicarbonate is fixed in the gel shell, and degrading bacteria are fixed in the core microsphere. The double-layer gel encapsulation structure isolates potassium persulfate and sodium bicarbonate, preventing potassium persulfate from being prematurely activated and rapidly consumed by sodium bicarbonate. At the same time, it also isolates potassium persulfate and degrading bacteria, avoiding damage to bacterial activity caused by the strong oxidizing potassium persulfate in the early stages of use.

[0065] The double-layer gel encapsulation structure not only achieves barrier between components but also controls the release sequence of each component, enabling the sequential chemical oxidation of potassium persulfate and biodegradation by degrading bacteria. Specifically, when the material is applied to the soil, the outermost gel shell first swells and dissolves under the influence of moisture. The surfactants within it solubilize pollutants, sodium bicarbonate creates an alkaline microenvironment to activate potassium persulfate, and sodium lactate provides the carbon source needed for microbial reproduction. Subsequently, potassium persulfate in the middle layer is slowly released under alkaline conditions, oxidizing organic pollutants and converting them into easily biodegradable small-molecule intermediates. Finally, the inner core microspheres exert their biodegradation effect, and the attapulgite carrier fully adsorbs and enriches the intermediates produced by potassium persulfate oxidation. The loaded degrading bacteria then biomineralize the enriched intermediates.

[0066] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0067] This invention first uses calcium chloride for primary cross-linking to form a core microsphere containing highly efficient petroleum hydrocarbon-degrading bacteria, with attapulgite powder as a carrier. Then, calcium lactate is used for secondary cross-linking to form an intermediate layer encapsulating potassium persulfate on the surface of the core microspheres. Finally, calcium chloride is used for tertiary cross-linking to form a gel shell containing sodium lactate, sodium bicarbonate, and surfactants. During the remediation process, the gel shell first contacts the soil environment. The surfactants in the gel solubilize pollutants, and the dissolution of sodium bicarbonate creates a slightly alkaline environment in the surrounding soil, triggering the potassium persulfate treatment. Sodium lactate provides the carbon source needed for microbial growth and reproduction. Subsequently, the potassium persulfate in the intermediate layer slowly diffuses, generating free radicals in the slightly alkaline environment, chemically oxidizing the pollutants and converting them into easily biodegradable small-molecule intermediates. Finally, the highly efficient petroleum hydrocarbon-degrading bacteria loaded in the core microspheres are activated and released, spreading and colonizing in the soil, mineralizing the intermediates adsorbed and enriched by the attapulgite. Chemical oxidation alone cannot completely mineralize organic pollutants and will produce intermediate products; while biodegradation alone has low efficiency in treating organic pollutants. This invention combines chemical oxidation and biodegradation, achieving the complementary advantages of the two treatment processes. Attached Figure Description

[0068] Figure 1 The following is a flowchart of the preparation process of the gel sustained-release repair materials provided in Examples 1-5 of this invention;

[0069] Figure 2 This is a scanning electron microscope image of the cross-sectional structure of the gel sustained-release repair material prepared in Example 1 of the present invention. Detailed Implementation

[0070] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0071] Example 1

[0072] This embodiment provides a method for preparing a gel-based slow-release remediation material for organically contaminated soil, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0073] (1) In a clean bench, scrape a small amount of freeze-dried Pseudomonas putida KT2440 strain powder with a sterile inoculation loop, streak it onto an LB solid medium plate, and incubate it upside down at 30°C for 2 days until a single colony grows. Pick a plump single colony with a neat edge with a sterile inoculation loop and inoculate it into LB liquid medium. Incubate it with shaking at 28°C and 150 rpm until the late logarithmic growth stage. Centrifuge at 3°C ​​and 7000 rpm, collect the centrifuged cells, add them to sterile physiological saline, disperse them evenly, and centrifuge again at 3°C ​​and 7000 rpm. Collect the centrifuged cells and add them to physiological saline to prepare a solution with a concentration of 1×10⁻⁶. 9 CFU / mL bacterial suspension;

[0074] Attapulgite was dried at 100℃ for 2 hours, then pulverized and passed through a 200-mesh sieve to obtain attapulgite powder. The attapulgite powder was dispersed in a bacterial suspension at a solid-liquid ratio of 1g:1mL, and the suspension was shaken and adsorbed at 80rpm for 2 hours. Then, it was centrifuged at 3℃ and 4000rpm for 6 minutes, and the precipitate was collected, which was the complex. The complex was mixed with a 1.5wt% sodium alginate solution at a solid-liquid ratio of 1g:3.5mL to obtain the core slurry. The core slurry was dropped into a 2wt% calcium chloride solution through a syringe with a needle inner diameter of 1mm, and gelled for 25 minutes to obtain core microspheres.

[0075] (2) Mix potassium persulfate, calcium lactate and deionized water evenly to obtain a crosslinking solution. The mass fraction of potassium persulfate in the crosslinking solution is 5wt% and the mass fraction of calcium lactate is 2wt%. Soak the core microspheres in the crosslinking solution at 5℃ and let them stand for crosslinking for 25min under the dark at 5℃. After filtration and washing, the intermediate microspheres are obtained.

[0076] (3) Sodium alginate, sodium lactate, sodium bicarbonate, Tween-80 and deionized water were mixed evenly to obtain a coating solution. The mass fraction of sodium alginate in the coating solution was 2 wt%, the mass fraction of sodium lactate was 4 wt%, the mass fraction of sodium bicarbonate was 4 wt%, and the mass fraction of Tween-80 was 0.15 wt%. The intermediate microspheres were soaked in the coating solution for 20 min, filtered out and then soaked again in a calcium chloride solution with a mass fraction of 1.5 wt%. The solution was left to stand for 50 min, then filtered out and washed. The solution was left to stand and solidify at 4 °C for 6 h. Finally, the solution was air-dried at 28 °C until the water content of the material was 15%, thus obtaining the gel sustained-release repair material.

[0077] Figure 2 The image shows a scanning electron microscope (SEM) image of the cross-sectional structure of the gel sustained-release repair material prepared in this embodiment. As can be clearly seen from the image, the structure consists of a core microsphere, an intermediate layer, and a gel shell, from the inside out.

[0078] Example 2

[0079] This embodiment provides a method for preparing a gel-based slow-release remediation material for organically contaminated soil, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0080] (1) In a clean bench, scrape a small amount of freeze-dried Pseudomonas putida KT2440 strain powder with a sterile inoculation loop, streak it onto an LB solid medium plate, and incubate it upside down at 30°C for 2 days until a single colony grows. Pick a plump single colony with neat edges with a sterile inoculation loop and inoculate it into LB liquid medium. Incubate it with shaking at 29°C and 160 rpm until the late logarithmic growth stage. Centrifuge at 3.5°C and 7200 rpm, collect the centrifuged cells, add them to sterile physiological saline, disperse them evenly, and centrifuge again at 3.5°C and 7200 rpm. Collect the centrifuged cells and add them to physiological saline to prepare a solution with a concentration of 2×10⁻⁶. 9 CFU / mL bacterial suspension;

[0081] Attapulgite was dried at 102℃ for 2 hours, then pulverized and passed through a 200-mesh sieve to obtain attapulgite powder. The attapulgite powder was dispersed in a bacterial suspension at a solid-liquid ratio of 1g:1.2mL, and the suspension was shaken and adsorbed at 85rpm for 1.8 hours. Then, the suspension was centrifuged at 3.5℃ and 4200rpm for 5.5 minutes, and the precipitate was collected as the complex. The complex was mixed with a 1.8wt% sodium alginate solution at a solid-liquid ratio of 1g:3.2mL to obtain the core slurry. The core slurry was dropped into a 2.2wt% calcium chloride solution through a syringe with a needle inner diameter of 1mm, and gelled for 22 minutes to obtain core microspheres.

[0082] (2) Potassium persulfate, calcium lactate and deionized water were mixed evenly to obtain a crosslinking solution. The mass fraction of potassium persulfate in the crosslinking solution was 5.2 wt% and the mass fraction of calcium lactate was 2.2 wt%. The core microspheres were immersed in the crosslinking solution at 6°C and allowed to stand for crosslinking for 28 min under the dark at 6°C. After filtration and washing, the intermediate microspheres were obtained.

[0083] (3) Sodium alginate, sodium lactate, sodium bicarbonate, Tween-80 and deionized water were mixed evenly to obtain a coating solution. The mass fraction of sodium alginate in the coating solution was 2.2 wt%, the mass fraction of sodium lactate was 4.2 wt%, the mass fraction of sodium bicarbonate was 4.2 wt%, and the mass fraction of Tween-80 was 0.18 wt%. The intermediate microspheres were soaked in the coating solution for 18 min, filtered out and then soaked again in a calcium chloride solution with a mass fraction of 1.6 wt%. The solution was allowed to stand for 48 min, then filtered out and washed. The solution was allowed to stand and solidify at 5 °C for 6.5 h. Finally, the solution was air-dried at 28 °C until the water content of the material was 13%, thus obtaining the gel sustained-release repair material.

[0084] Example 3

[0085] This embodiment provides a method for preparing a gel-based slow-release remediation material for organically contaminated soil, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0086] (1) In a clean bench, scrape a small amount of freeze-dried Pseudomonas putida KT2440 strain powder with a sterile inoculation loop, streak it onto an LB solid medium plate, and incubate it upside down at 30°C for 2 days until a single colony grows. Pick a plump single colony with neat edges with a sterile inoculation loop and inoculate it into LB liquid medium. Incubate it with shaking at 30°C and 170 rpm until the late logarithmic growth stage. Centrifuge at 4°C and 7500 rpm, collect the centrifuged cells, add them to sterile physiological saline, disperse them evenly, and centrifuge again at 4°C and 7500 rpm. Collect the centrifuged cells and add them to physiological saline to prepare a solution with a concentration of 3×10⁻⁶. 9 CFU / mL bacterial suspension;

[0087] Attapulgite was dried at 105℃ for 2 hours, then pulverized and passed through a 200-mesh sieve to obtain attapulgite powder. The attapulgite powder was dispersed in a bacterial suspension at a solid-liquid ratio of 1g:1.5mL, and the suspension was shaken and adsorbed at 90rpm for 1.5 hours. Then, the suspension was centrifuged at 4℃ and 4500rpm for 5 minutes, and the precipitate was collected as the complex. The complex was mixed with a 2wt% sodium alginate solution at a solid-liquid ratio of 1g:3mL to obtain the core slurry. The core slurry was dropped into a 2.5wt% calcium chloride solution through a syringe with a needle inner diameter of 1.1mm, and gelled for 20 minutes to obtain core microspheres.

[0088] (2) Potassium persulfate, calcium lactate and deionized water were mixed evenly to obtain a crosslinking solution. The mass fraction of potassium persulfate in the crosslinking solution was 5.5 wt% and the mass fraction of calcium lactate was 2.5 wt%. The core microspheres were immersed in the crosslinking solution at 7°C and allowed to stand for crosslinking for 30 min under the dark at 7°C. After filtration and washing, the intermediate microspheres were obtained.

[0089] (3) Sodium alginate, sodium lactate, sodium bicarbonate, Tween-80 and deionized water were mixed evenly to obtain a coating solution. The mass fraction of sodium alginate in the coating solution was 2.5 wt%, the mass fraction of sodium lactate was 4.5 wt%, the mass fraction of sodium bicarbonate was 4.5 wt%, and the mass fraction of Tween-80 was 0.2 wt%. The intermediate microspheres were soaked in the coating solution for 17 min, filtered out and then soaked again in a calcium chloride solution with a mass fraction of 1.7 wt%. The solution was allowed to stand for 45 min, then filtered out and washed. The solution was allowed to stand and solidify at 6 °C for 7 h. Finally, the solution was air-dried at 29 °C until the water content of the material was 12% to obtain the gel sustained-release repair material.

[0090] Example 4

[0091] This embodiment provides a method for preparing a gel-based slow-release remediation material for organically contaminated soil, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0092] (1) In a clean bench, scrape a small amount of freeze-dried Pseudomonas putida KT2440 strain powder with a sterile inoculation loop, streak it onto an LB solid medium plate, and incubate it upside down at 30°C for 2 days until a single colony grows. Pick a plump single colony with neat edges with a sterile inoculation loop and inoculate it into LB liquid medium. Incubate it with shaking at 31°C and 180 rpm until the late logarithmic growth stage. Centrifuge at 4.5°C and 7800 rpm, collect the centrifuged cells, add them to sterile physiological saline, disperse them evenly, and centrifuge again at 4.5°C and 7800 rpm. Collect the centrifuged cells and add them to physiological saline to prepare a solution with a concentration of 4×10⁻⁶. 9 CFU / mL bacterial suspension;

[0093] Attapulgite was dried at 108℃ for 2 hours, then pulverized and passed through a 200-mesh sieve to obtain attapulgite powder. The attapulgite powder was dispersed in a bacterial suspension at a solid-liquid ratio of 1g:1.8mL, and the suspension was shaken and adsorbed at 95rpm for 1.2 hours. Then, it was centrifuged at 4.4℃ and 4800rpm for 4.5 minutes, and the precipitate was collected as the complex. The complex was mixed with a 2.2wt% sodium alginate solution at a solid-liquid ratio of 1g:2.8mL to obtain the core slurry. The core slurry was dropped into a 2.8wt% calcium chloride solution through a syringe with a needle inner diameter of 1.2mm, and gelled for 18 minutes to obtain core microspheres.

[0094] (2) Potassium persulfate, calcium lactate and deionized water were mixed evenly to obtain a crosslinking solution. The mass fraction of potassium persulfate in the crosslinking solution was 5.8 wt% and the mass fraction of calcium lactate was 2.8 wt%. The core microspheres were immersed in the crosslinking solution at 8°C and allowed to crosslink for 32 min under light-proof conditions at 8°C. After filtration and washing, the intermediate microspheres were obtained.

[0095] (3) Sodium alginate, sodium lactate, sodium bicarbonate, Tween-80 and deionized water were mixed evenly to obtain a coating solution. The mass fraction of sodium alginate in the coating solution was 2.8 wt%, the mass fraction of sodium lactate was 4.8 wt%, the mass fraction of sodium bicarbonate was 4.8 wt%, and the mass fraction of Tween-80 was 0.22 wt%. The intermediate microspheres were soaked in the coating solution for 16 min, filtered out and then soaked again in a calcium chloride solution with a mass fraction of 1.8 wt%. The solution was allowed to stand for 42 min, then filtered out and washed. The solution was allowed to stand and solidify at 7 °C for 7.5 h. Finally, the solution was air-dried at 29 °C until the water content of the material was 11%, thus obtaining the gel sustained-release repair material.

[0096] Example 5

[0097] This embodiment provides a method for preparing a gel-based slow-release remediation material for organically contaminated soil, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0098] (1) In a clean bench, scrape a small amount of freeze-dried Pseudomonas putida KT2440 strain powder with a sterile inoculation loop, streak it onto an LB solid medium plate, and incubate it upside down at 30°C for 2 days until a single colony grows. Pick a plump single colony with a neat edge with a sterile inoculation loop and inoculate it into LB liquid medium. Incubate it with shaking at 32°C and 200 rpm until the late logarithmic growth stage. Centrifuge at 5°C and 8000 rpm, collect the centrifuged cells, add them to sterile physiological saline, disperse them evenly, and centrifuge again at 5°C and 8000 rpm. Collect the centrifuged cells and add them to physiological saline to prepare a solution with a concentration of 5×10⁻⁶. 9CFU / mL bacterial suspension;

[0099] Attapulgite was dried at 110℃ for 2 hours, then pulverized and passed through a 200-mesh sieve to obtain attapulgite powder. The attapulgite powder was dispersed in a bacterial suspension at a solid-liquid ratio of 1g:2mL, and the suspension was shaken and adsorbed at 100rpm for 1 hour. Then, it was centrifuged at 5℃ and 5000rpm for 4 minutes, and the precipitate was collected, which was the complex. The complex was mixed with a 2.5wt% sodium alginate solution at a solid-liquid ratio of 1g:2.5mL to obtain the core slurry. The core slurry was dropped into a 3wt% calcium chloride solution through a syringe with a needle inner diameter of 1.2mm, and gelled for 15 minutes to obtain core microspheres.

[0100] (2) Potassium persulfate, calcium lactate and deionized water were mixed evenly to obtain a crosslinking solution. The mass fraction of potassium persulfate in the crosslinking solution was 6 wt% and the mass fraction of calcium lactate was 3 wt%. The core microspheres were immersed in the crosslinking solution at 10°C and allowed to stand for crosslinking at 10°C in the dark for 35 min. After filtration and washing, the intermediate microspheres were obtained.

[0101] (3) Sodium alginate, sodium lactate, sodium bicarbonate, Tween-80 and deionized water are mixed evenly to obtain a coating solution. The mass fraction of sodium alginate in the coating solution is 3wt%, the mass fraction of sodium lactate is 5wt%, the mass fraction of sodium bicarbonate is 5wt%, and the mass fraction of Tween-80 is 0.25wt%. The intermediate microspheres are soaked in the coating solution for 15min, filtered out and then soaked in a calcium chloride solution with a mass fraction of 2wt% for 40min. After standing, they are filtered out, washed, and solidified at 8℃ for 8h. Finally, they are air-dried at 30℃ until the water content of the material is 10% to obtain the gel sustained-release repair material.

[0102] Comparative Example 1

[0103] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that in step (1), the mass fraction of calcium chloride solution is adjusted to 1 wt%, while other operation steps and process parameters are exactly the same as in Embodiment 1.

[0104] Comparative Example 2

[0105] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that in step (1), the mass fraction of calcium chloride solution is adjusted to 5 wt%, while other operation steps and process parameters are exactly the same as in Embodiment 1.

[0106] Comparative Example 3

[0107] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that in step (1), the bacterial suspension is omitted, and the attapulgite powder is mixed evenly with sodium alginate solution to obtain a core slurry. The slurry is then dropped into calcium chloride solution to gel and solidify, resulting in core microspheres. The core microspheres in the final gel slow-release remediation material only contain attapulgite powder and are not loaded with degrading bacteria. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0108] Comparative Example 4

[0109] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that step (2) is omitted, and the core microspheres obtained in step (1) are directly immersed in the coating liquid. The final gel slow-release remediation material consists of core microspheres and a gel shell covering the surface. There is no intermediate layer between the core microspheres and the gel shell. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0110] Comparative Example 5

[0111] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that in step (3), the coating solution does not contain sodium lactate, while the other operation steps and process parameters are exactly the same as in Embodiment 1.

[0112] Comparative Example 6

[0113] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that in step (3), the coating solution does not contain sodium bicarbonate, while the other operation steps and process parameters are exactly the same as in Embodiment 1.

[0114] Comparative Example 7

[0115] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that step (3) is omitted, and the intermediate microspheres obtained in step (2) are air-dried at 28°C until the water content is 15%. The final gel slow-release remediation material consists of a core microsphere and an intermediate layer. The surface of the intermediate layer is not covered with a gel shell. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0116] Comparative Example 8

[0117] This embodiment provides a method for preparing a gel slow-release remediation material for organically contaminated soil. The difference from Embodiment 1 is that steps (2) and (3) are omitted. The core microspheres obtained in step (1) are air-dried at 28°C until the water content is 15% to obtain the gel slow-release remediation material. The surface of the core microspheres is not covered with an intermediate layer and a gel shell. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0118] Application examples

[0119] Contaminated soil samples were taken from around the chemical plant (blank group). The gel-release remediation material prepared in the examples and comparative examples was evenly spread on the surface of the contaminated soil at a mass ratio of 1:100. The mixture was thoroughly mixed, and the soil moisture content was adjusted and maintained within the field water holding capacity range of 60-80%. At the same time, the soil temperature was controlled within the range of 20-30°C. The remediation was carried out for 60 days, and the soil was tilled regularly throughout the entire remediation period.

[0120] The concentrations of benzo[a]pyrene, benzo[a]anthracene, benzo[b]fluoranthracene, and benzo[k]fluoranthracene in contaminated soil and remediated soil were detected in accordance with the industry standard HJ805-2016 "Determination of polycyclic aromatic hydrocarbons in soil and sediment by gas chromatography-mass spectrometry".

[0121] The test results are shown in Table 1.

[0122] Table 1

[0123] Benzo[a]pyrene (mg / kg) Benzo[a]anthracene (mg / kg) Benzo[b]fluoranthene (mg / kg) Benzo[k]fluoranthene (mg / kg) Example 1 0.12 0.48 0.19 0.37 Example 2 0.14 0.51 0.22 0.39 Example 3 0.11 0.46 0.18 0.36 Example 4 0.13 0.49 0.21 0.38 Example 5 0.15 0.53 0.23 0.4 Comparative Example 1 0.87 1.72 1.18 1.49 Comparative Example 2 0.92 1.81 1.24 1.55 Comparative Example 3 1.28 2.44 1.75 2.14 Comparative Example 4 1.73 3.22 2.36 2.85 Comparative Example 5 0.68 1.39 0.93 1.2 Comparative Example 6 1.85 3.44 2.53 3.04 Comparative Example 7 0.95 1.86 1.3 1.62 Comparative Example 8 2.31 4.24 3.16 3.77 Blank group 3.8 6.85 5.2 6.12

[0124] The national standard GB 36600-2018, "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control (Trial Implementation)," stipulates the following screening values ​​for soil pollution risk in construction land (Class I land): benzo[a]pyrene ≤ 0.55 mg / kg, benzo[a]anthracene ≤ 5.5 mg / kg, benzo[b]fluoranthracene ≤ 5.5 mg / kg, and benzo[k]fluoranthracene ≤ 55 mg / kg. As can be seen from the test data provided in Table 1, the organic matter concentrations in the remediated soils of Examples 1-5 are all far lower than the screening values ​​specified in the national standard GB 36600-2018.

[0125] The test data from Example 1, Comparative Example 1, and Comparative Example 2 show that the calcium chloride concentration in Comparative Example 1 was too low, resulting in a loose calcium alginate gel network structure with poor mechanical strength, and the degradation bacteria loaded in the core microspheres were easily lost. The calcium chloride concentration in Comparative Example 2 was too high, causing an excessively dense hard shell to form instantly on the surface of the core microspheres, hindering the diffusion of calcium ions into the interior, ultimately forming a hard-outer-soft-inner structure, leading to cracking of the core microspheres. Furthermore, the formation of a hard shell on the surface reduces the number of free carboxyl functional groups, affecting the subsequent secondary cross-linking of calcium lactate.

[0126] The test data from Examples 1, 3, 4, 7, and 8 show that: Comparative Example 3 omitted the highly efficient petroleum hydrocarbon degrading bacteria, resulting in the final product's inability to exert its biodegradation capacity, and the intermediate products generated by chemical oxidation could not be completely mineralized. Comparative Example 4 omitted the potassium persulfate-loaded intermediate layer, resulting in the final product's inability to exert its chemical oxidation capacity, and organic pollutants could not be effectively converted into easily biodegradable small molecules; the degrading bacteria could not achieve complete mineralization of organic pollutants. Comparative Example 7 omitted the outermost gel shell, directly exposing the product to the soil environment. The intermediate layer was the first to come into contact with the soil, and the fixed potassium persulfate in it was prematurely activated and consumed by the soil environment, affecting the persistence of the product's chemical oxidation capacity. At the same time, the strong oxidizing environment generated by potassium persulfate also damaged the activity of the degrading bacteria in the core microspheres. Comparative Example 8 omitted both the intermediate layer and the gel shell, leaving only the core microspheres loaded with degrading bacteria. It lost the chemical oxidation capacity of the intermediate layer and the carbon source supply from the gel shell, making it difficult for the degrading bacteria to fully exert their biodegradation capacity.

[0127] The test data from Examples 1, 5, and 6 show that Comparative Example 5 did not add sodium lactate to the gel shell, resulting in the remediation material being unable to provide a carbon source for soil microorganisms and the degrading bacteria in the core. This affected the proliferation and metabolic activity of the microorganisms, reducing the product's biodegradability. Comparative Example 6 did not add sodium bicarbonate to the gel shell, preventing the effective activation of potassium persulfate to generate sulfate free radicals. Even with the presence of potassium persulfate, the product's chemical oxidation capacity was still affected.

[0128] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a gel-based slow-release remediation material for organically contaminated soil, characterized in that, The preparation method includes: (I) The highly efficient petroleum hydrocarbon degrading bacteria were inoculated into LB liquid medium and cultured by shaking. After centrifugation and resuspension, a bacterial suspension was obtained. Attapulgite powder was dispersed in the bacterial suspension, and the mixture was shaken to adsorb and centrifuged to obtain a complex. The complex was mixed evenly with sodium alginate solution to obtain a core slurry. The core slurry was dropped into calcium chloride solution through a syringe and gelled to obtain core microspheres. (II) Potassium persulfate, calcium lactate and deionized water are mixed evenly to obtain a crosslinking solution; the core microspheres are immersed in the pre-cooled crosslinking solution, and crosslinked under light-protected conditions. The mixture is then filtered out and washed to obtain the intermediate microspheres. (III) Sodium alginate, sodium lactate, sodium bicarbonate, surfactant and deionized water are mixed evenly to obtain a coating solution; the intermediate microspheres are immersed in the coating solution, filtered out and then immersed in calcium chloride solution, allowed to stand for crosslinking, then filtered out, washed, allowed to stand for curing and dried to obtain the gel sustained-release repair material.

2. The preparation method according to claim 1, characterized in that, In step (I), the temperature for the oscillation culture is 28~32℃; The rotation speed of the oscillation culture is 150~200 rpm; The oscillating culture was carried out to the late logarithmic growth stage; The centrifugation temperature is 3~5℃; The centrifuge speed is 7000~8000 rpm.

3. The preparation method according to claim 1, characterized in that, In step (I), the resuspension process includes: Collect the centrifuged bacterial cells, add them to sterile physiological saline, disperse them evenly, centrifuge again, collect the centrifuged bacterial cells, add them to physiological saline, and prepare the bacterial suspension; The concentration of the bacterial suspension is 1×10⁻⁶. 9 ~5×10 9 CFU / mL.

4. The preparation method according to claim 1, characterized in that, In step (I), the solid-liquid ratio of the attapulgite powder to the bacterial suspension is 1g:(1~2)mL; The rotation speed of the oscillation adsorption is 80~100 rpm; The oscillation adsorption time is 1~2 hours; The centrifugation temperature is 3~5℃; The centrifuge speed is 4000~5000 rpm; The centrifugation time is 4-6 minutes.

5. The preparation method according to claim 1, characterized in that, In step (I), the sodium alginate solution has a mass fraction of 1.5~2.5 wt%. The solid-liquid ratio of the complex to the sodium alginate solution is 1 g:(2.5~3.5) mL; The syringe needle has an inner diameter of 1~1.2mm; The calcium chloride solution has a mass fraction of 2-3 wt%. The gel solidification time is 15~25 minutes.

6. The preparation method according to claim 1, characterized in that, In step (II), the mass fraction of potassium persulfate in the crosslinking solution is 5-6 wt%. The mass fraction of calcium lactate in the crosslinking solution is 2-3 wt%. The crosslinking solution is precooled to 5~10℃; The core microspheres are allowed to undergo static cross-linking in the cross-linking solution for 25-35 minutes. The core microspheres are statically crosslinked in the crosslinking solution at a temperature of 5~10℃.

7. The preparation method according to claim 1, characterized in that, In step (III), the mass fraction of sodium alginate in the coating solution is 2-3 wt%. The mass fraction of sodium lactate in the coating solution is 4-5 wt%. The mass fraction of sodium bicarbonate in the coating solution is 4-5 wt%. The surfactant in the coating solution has a mass fraction of 0.15~0.25 wt%. The surfactant includes Tween-80; The intermediate microspheres are immersed in the coating solution for 15-20 minutes.

8. The preparation method according to claim 1, characterized in that, In step (III), the mass fraction of the calcium chloride solution is 1.5~2 wt%. The intermediate microspheres are allowed to crosslink in the calcium chloride solution for 40-50 minutes. The temperature for static curing is 4~8℃; The static curing time is 6-8 hours; The drying process involves air-drying the material at 28-30°C until the moisture content is 10-15%.

9. A gel-release remediation material for organically contaminated soil prepared by the preparation method according to any one of claims 1 to 8.

10. The gel-release repair material according to claim 9, characterized in that, The gel sustained-release repair material includes a core microsphere, and an intermediate layer and a gel shell that are sequentially coated on the surface of the core microsphere from the inside out. The core microspheres contain attapulgite powder and highly efficient petroleum hydrocarbon degrading bacteria loaded thereon, the intermediate layer contains potassium persulfate, and the gel shell contains sodium lactate, sodium bicarbonate, and surfactant.

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