Method for reinforced remediation of soil polluted by polycyclic aromatic hydrocarbon through small molecular acid

Abstract

The invention belongs to the technical field of soil remediation, and discloses a method for reinforced remediation of soil polluted by polycyclic aromatic hydrocarbons (PAHs) with small molecular acids, which comprises the following steps: adding the small molecular acids CA, MA, TA or OA into PAHs-polluted soil, fixing air humidity and temperature, and fully reacting in a climate box in a dark place for 1-60 days to finish remediation of the polluted soil. According to the method, natural organic acid is adopted to achieve a good degradation effect on soil polluted by PAHs, operation is easy, and the method is suitable for large-scale application and popularization. According to the method, the defect that a traditional chemical oxidation remediation technology has great damage to soil is overcome, the activity of Fe (II) in the soil is enhanced, circulation of Fe (II) / Fe (III) in a reaction system is promoted, the output of ROS is remarkably increased, and efficient removal and mineralization of PAHs in the contaminated soil are achieved. The method can be quickly and efficiently carried out at normal temperature and normal pressure without adjusting the pH value of soil.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology and relates to a method for remediating polycyclic aromatic hydrocarbon pollution in soil using small molecule acid enhancement. Background Technology

[0002] Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds composed of two or more benzene rings, widely distributed in the environment. PAHs mainly originate from anthropogenic activities, such as incomplete combustion or pyrolysis of organic matter and oil pollution. Due to their high hydrophobicity, persistence, and difficulty in biodegradation, PAHs easily accumulate in soil and can persist for decades. PAHs are one of the most common organic pollutants in Chinese soils, and high concentrations and high-ring-number PAHs often accumulate in long-term polluted soils. The concentration of PAHs in Chinese topsoils can reach hundreds to thousands of micrograms per kilogram. Given the carcinogenic, teratogenic, mutagenic, and genotoxic effects of PAHs, they pose a significant risk to human health (Zhang Y, Peng C, Guo Z, et al. Polycyclic aromatic hydrocarbons in urbansoils of China: Distribution, influencing factors, health risk and regressionprediction[J]. Environmental Pollution, 2019,254:112930.). Therefore, the remediation of PAH-contaminated soil has become an important research hotspot and a matter of public concern. Currently, physical and biological remediation are the most commonly used technologies for remediation of soils with high concentrations of PAHs, but these methods have drawbacks such as long remediation cycles, high energy consumption, and difficulty in reusing the remediated soil. Therefore, there is an urgent need to develop a new, rapid, efficient, safe, and economical remediation technology for PAH pollution.

[0003] Chemical oxidation remediation of PAHs in soil is currently a mainstream soil remediation technology, capable of degrading toxic or highly toxic organic pollutants into less toxic or non-toxic small-molecule organic compounds. The Fenton reaction is one of the most popular chemical oxidation technologies, based on the reaction of Fe(II) and hydrogen peroxide (H2O2) to generate highly oxidizing free radicals, which then degrade pollutants. However, traditional chemical oxidation or Fenton technologies are generally highly destructive, making it difficult to reuse the remediated soil in the short term, and also suffer from high energy consumption and significant risks. To address these drawbacks, enhanced natural attenuation technology based on the Fenton principle is considered a more environmentally sustainable and cost-effective in-situ remediation method. This method includes adsorption, volatilization, dilution, biodegradation, and abiotic degradation. Biodegradation and abiotic degradation, in particular, can truly eliminate PAHs in soil. However, high-molecular-weight PAHs are toxic and poorly soluble in water, making them difficult to biodegrade. Studies have shown that reactive oxygen species (ROS), especially hydroxyl radicals (•OH), are the main factors contributing to the abiotic degradation of PAHs in soil. In these processes, ROS can be generated through photochemical reactions of dissolved organic matter and Fe(II)-induced Fenton-like reactions. However, naturally generated ROS in soil has limited ability to degrade PAHs. Therefore, based on the Fenton principle, selecting green soil activators can enhance the degradation efficiency of PAHs in soil (Zhang X, Gu X, Lu S, et al. Application of ascorbic acid to enhance trichloroethene degradation by Fe(III)-activated calcium peroxide[J]. Chemical Engineering Journal, 2017,325(6):188-198.).

[0004] Low molecular weight organic acids (LMWOAs) are ubiquitous in soils, primarily originating from plant root exudates and the microbial decomposition of organic matter. These organic acids are considered important reactive components and significantly influence the generation of reactive oxygen species (ROS) in natural soils. LMWOAs, such as citric acid (CA), malic acid (MA), oxalic acid (OA), and tartaric acid (TA), typically coexist with soil minerals and possess a strong chelating ability with transition metal cations (such as Fe(III)), thereby enhancing soil ROS generation. For example, OA has been reported to react with iron minerals, accelerating ROS generation to degrade phenolic compounds. Among these organic acids, CA is an environmentally friendly redox agent that can influence the migration and transformation, dissolution and sedimentation, and redox capacity of iron minerals in soil. For instance, CA can effectively activate hydrogen peroxide, promoting the oxidation cycle of iron in Fenton-like reactions. Simultaneously, soils rich in various transition metal elements significantly influence the transformation pathways of pollutants. (Wen N, Liu J, Qin W, et al. Critical roles of low-molecular-weight organic acid inenhancing hydroxyl radical production by ferrous oxidation on γ-Al₂O₃mineral surface[J]. Water Research, 2024,261:122052.). Therefore, it is reasonable to expect that low-molecular-weight acids can enhance the degradation efficiency of PAHs in soil. However, there are currently no reports on the promotion of PAH degradation efficiency by low-molecular-weight acids. Summary of the Invention

[0005] To address the aforementioned problem of PAHs remediation in soil, this invention provides a method for degrading high concentrations of PAHs in soil after activating the soil with a small-molecule acid. This method effectively overcomes the drawbacks of traditional chemical oxidation remediation, which causes significant soil damage, promotes the generation of ROS in the soil, and efficiently degrades PAHs in the soil. It also features simple operation, wide applicability, and low treatment costs.

[0006] The present invention adopts the following technical solution:

[0007] A method for remediating soil polycyclic aromatic hydrocarbon (PAH) pollution using small molecule acid enhancement includes the following steps:

[0008] Adding small-molecule organic acids to PAH-contaminated soil, fixing soil moisture, and allowing it to react fully at room temperature for 1-60 days (preferably 30 days) can complete the remediation of contaminated soil.

[0009] Furthermore, PAHs are one or more combinations of benzo[a]anthracene, benzo[a]pyrene, indo[1,2,3-cd]pyrene and dibenzo[a,h]anthracene.

[0010] Furthermore, the small molecule organic acid is CA, MA, TA, or OA, preferably CA.

[0011] Furthermore, the concentration of PAHs in the soil was 90–110 mg / kg.

[0012] Furthermore, the dosage of the small molecule acid is 10–50 mmol / g, preferably 40 mmol / g.

[0013] Furthermore, the soil pH is 4-9, preferably pH 7.

[0014] Furthermore, the air humidity in the system is 20%-70%, preferably 50%.

[0015] Using the above methods, the removal rate of most PAHs in the soil can be increased by more than 1.5 times within 15 days, and preferably by more than 2 times within 30 days.

[0016] The beneficial effects of this invention are:

[0017] (1) The present invention provides a method for degrading high concentrations of PAHs in soil. It only requires the use of readily available commercial small molecule acids to achieve good degradation effects on different types of soil contaminated by PAHs. The method is simple to operate and suitable for large-scale promotion and application.

[0018] (2) This method improves the disadvantage of slow generation of reactive oxygen species in soil by adding small molecule acid, which significantly increases the Fe(II) content in soil, promotes the Fe(II) / Fe(III) cycle in the reaction system, significantly increases the amount of •OH generated, and greatly shortens the reaction time. It achieves efficient removal and mineralization of PAHs in polluted soil while changing the inherent physicochemical properties of soil as little as possible.

[0019] (3) This invention can be carried out quickly and efficiently at normal temperature and pressure. Furthermore, the small molecule acid added in this invention is inexpensive, environmentally friendly, biodegradable, and does not cause secondary pollution, providing a broad application prospect for the harmless remediation of PAHs-contaminated soil. Attached Figure Description

[0020] Figure 1 The effects of four small molecule acid systems on PAHs in soil were studied.

[0021] Figure 2 The degradation effect of the CA system on PAHs pollution in different types of soil;

[0022] Figure 3 The effects of different concentrations of CA on the degradation of PAHs in soil;

[0023] Figure 4 The degradation effect of CA under different soil pH conditions.

[0024] Figure 5 To determine •OH in CA and blank soil systems using electron paramagnetic resonance (EPR) technology. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0026] Example 1

[0027] Benzo[a]pyrene (BaP) was selected as a typical PAH in soil, with a concentration of 100 mg / kg. 1 g of BaP-contaminated soil was weighed and placed in a 50 mL cylindrical glass vial, sealed with a Teflon cap, and wrapped with aluminum foil to avoid potential photomutation effects. The remediation effect of adding different organic acids on BaP-contaminated soil was investigated. The experimental systems included CA, MA, TA, OA, and a blank system. Soil pH, temperature, and air humidity were kept constant in all five systems. The degradation experiment was conducted in a climate chamber at 25°C in the dark. A parallel sample was taken at 0, 1, 3, 5, 7, 9, 15, and 30 days after the reaction. Immediately after sampling, 5 mL of methanol was added and the mixture was shaken for 1 min to completely quench the reaction. The total residual BaP content was determined by liquid chromatography (the recovery rate of BaP extracted from soil using the above steps was between 98% and 105%). Finally, the degradation rate of PAHs in the soil was calculated. The results are as follows: Figure 1 As shown, the degradation rate of BaP was 24% without the addition of small molecule acids. After adding CA, MA, TA, and OA, the degradation rates of BaP were 60%, 58%, 50%, and 53%, respectively. This indicates that different types of organic acids have varying effects on enhancing the degradation of PAHs. In contrast, the other three organic acids (MA, TA, and OA) were less effective than CA in promoting the degradation of PAHs. This difference in effectiveness likely stems from the different molecular structures of low molecular weight organic acids. It is generally believed that the functional group composition of organic acids (such as the number of α-hydroxy and carboxyl groups) directly determines their chemical activity and environmental effects. Among them, the number of α-hydroxy (α-OH) groups, as key reducing functional groups, directly affects the reducing power of organic acids, thus determining their potential to activate soil components and mediate ROS generation; while the number of carboxyl (-COOH) groups is mainly related to their acidity and complexing ability, altering the occurrence state and reactivity of pollutants by lowering environmental pH and integrating metal ions. Figure 1As shown, small molecule acids can enhance iron leaching in the soil system, promote the Fe(II) / Fe(III) cycle in the system, and activate H2O2 to generate more •OH. Further analysis using electron paramagnetic resonance (EPR) technology determined the ROS signals in the CA and blank systems, such as... Figure 1 As shown, the signal intensity of •OH in the CA system is much higher than that in the blank soil.

[0028] Example 2

[0029] 1 g of BaP-contaminated soil was weighed and placed in a 50 mL cylindrical glass vial, sealed with a Teflon cap, and wrapped with aluminum foil to avoid potential photomutation. The degradation experiment was conducted in a climate chamber at 25°C in the dark. The sacrificial bottle method was used; a parallel sample was taken at 0, 1, 3, 5, 7, 9, 15, and 30 days after the reaction. Immediately after sampling, 5 mL of methanol was added and the sample was shaken for 1 min to completely quench the reaction. The total residual BaP content was determined by liquid chromatography after treatment. The results are attached. Figure 2 As shown, the degradation of PAHs in seven different soils from various regions of China was demonstrated with and without the addition of CA. The soils used in the experiment came from different regions of China: Hainan (Soil-1), Chongqing (Soil-2), Jilin (Soil-3), Hebei (Soil-4), Heilongjiang (Soil-5), Yunnan (Soil-6), and Liaoning (Soil-7). The degradation effects of different types of PAHs varied in different soils, but the overall trend was not significantly different. Without CA, soil S1 showed the best degradation effect, with the overall degradation effect showing S1>S2>S6>S7>S5>S4>S3. This may be due to the lower SOM content and higher Fe content in soil S1. After adding CA, soil S7 showed the best degradation effect, with the overall degradation effect showing S7>S2>S6>S4>S1>S3>S5. The degradation effect of BaP changed significantly after adding CA, demonstrating that CA can react with soil components, thereby altering the soil's degradation capacity.

[0030] Example 3

[0031] 1 g of BaP-contaminated soil was weighed and placed in a 50 mL cylindrical glass vial, sealed with a Teflon cap, and wrapped with aluminum foil to avoid potential photomutation. To determine the optimal dosage of organic acid, CA was added at organic acid to soil ratios of 20 mmol / g, 40 mmol / g, and 60 mmol / g, respectively. The degradation experiment was conducted in a climate chamber at 25°C in the dark. The sacrificial bottle method was used; a parallel sample was taken at 0, 1, 3, 5, 7, 9, 15, and 30 days of reaction. Immediately after sampling, 5 mL of methanol was added and the mixture was shaken for 1 min to completely quench the reaction. The total residual BaP content was determined by liquid chromatography after treatment. (See attached image) Figure 3 As the CA concentration increased from 20 to 40 mmol / g, the BaP removal rate significantly improved from 50% to 60%. However, further increasing the CA concentration to 60 mmol / g inhibited BaP removal. This is likely because excess CA removes •OH. Therefore, the optimal addition level for the small molecule acid is 40 mmol / g.

[0032] Example 4

[0033] 1 g of BaP-contaminated soil was weighed and placed in a 50 mL cylindrical glass vial, sealed with a Teflon cap, and wrapped with aluminum foil to avoid potential photomutation. 40 mmol / g CA was added to the vial. The degradation experiment was conducted in a climate chamber at 25°C in the dark. The sacrificial bottle method was used; a set of parallel samples were taken at 0, 1, 3, 5, 7, 9, 15, and 30 days after the reaction. Immediately after sampling, 5 mL of methanol was added and the mixture was shaken for 1 min to completely quench the reaction. The total residual BaP content was determined by liquid chromatography after treatment. The results are attached. Figure 4 As shown, the results indicate that in the control soil system without added organic acids, a decrease in initial soil pH significantly promoted BaP degradation. Specifically, when the initial soil pH decreased from 7 (neutral) to 5 (acidic), the BaP degradation rate increased by 18%; conversely, when the pH increased from 7 to 9 (alkaline), the degradation rate decreased by 8%. This phenomenon clearly reveals that an acidic environment is more conducive to BaP degradation, possibly because lower pH conditions promote the dissolution of certain metal oxides (such as iron and manganese oxides) in the soil, thereby enhancing the transition metal-based Fenton-like reaction. When organic acid (CA) was introduced into the soil, the BaP degradation efficiency was improved to varying degrees compared to the control group at all tested pH levels, confirming the general promoting effect of organic acids on pollutant degradation. Furthermore, at soil pH 7, organic acids showed the best effect in enhancing PAH degradation.

[0034] Example 5

[0035] 1 g of BaP-contaminated soil was weighed and placed in a 50 mL cylindrical glass vial, sealed with a Teflon cap, and wrapped with aluminum foil to avoid potential photomutation. 40 mmol / g CA was added to the vial. The degradation experiment was conducted in a climate chamber at 25°C in the dark. The generation of ROS in the soil during BaP degradation was identified, and ROS generation was determined using EPR. (See attached image) Figure 5 As shown, the EPR spectrum indicates that both DMPO-O2 adduct and DMPO-OH signals with ultrafine splitting (g = 2.0064) were observed in the contaminated soil, regardless of the addition of CA. After the addition of CA, •OH and O2... •- The signal was significantly stronger than that without CA, with a particularly significant enhancement in the •OH signal, which preliminarily suggests that CA is beneficial to the formation of ROS in the soil. Some studies indicate that CA may alter the speciation of Fe(II) / Fe(III) in the soil and accelerate the Fe(II) / Fe(III) redox cycle, thereby promoting electron transfer from soil minerals to O2. According to the Haber-Weiss mechanism, Fe(II) is oxidized to O2. •- It reacts with H2O2, and then H2O2 decomposes to produce •OH.

Claims

1. A method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement, characterized in that, The steps include the following: Adding small-molecule organic acids to PAH-contaminated soil and fixing soil moisture, allowing it to react fully at room temperature for 1-60 days, can complete the remediation of contaminated soil.

2. The method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement according to claim 1, characterized in that, The PAHs mentioned are one or more combinations of benzo[a]anthracene, benzo[a]pyrene, indo[1,2,3-cd]pyrene, and dibenzo[a,h]anthracene.

3. The method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement according to claim 1, characterized in that, The small molecule organic acid is CA, MA, TA or OA.

4. The method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement according to claim 1, characterized in that, The concentration of the PAHs in the soil is 90–110 mg / kg.

5. The method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement according to claim 1, characterized in that, The dosage of the small molecule acid is 10–50 mmol / g, preferably 40 mmol / g.

6. The method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement according to claim 1, characterized in that, The soil pH is 4-9.

7. The method for remediating soil polycyclic aromatic hydrocarbon pollution using small molecule acid enhancement according to claim 1, characterized in that, The air humidity is 20%-70%.

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