A method and composition for removing endogenous polycyclic aromatic hydrocarbons from biochar with humic acid and oxalic acid

Abstract

The present invention discloses a method and composition for removing endogenous polycyclic aromatic hydrocarbons (PAHs) from biochar using humic acid and oxalic acid. The method comprises the following steps: adding humic acid and oxalic acid to soil containing biochar for treatment to degrade the endogenous PAHs in the biochar. This method not only reduces the total content of endogenous PAHs in the biochar but also significantly promotes the degradation of both low-ring and high-ring PAHs. In particular, it significantly increases the degradation rate of high-ring PAHs, with a particularly strong degradation effect on fluoranthene and chrysene.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural solid waste treatment and resource utilization, and specifically to a method and composition for removing endogenous polycyclic aromatic hydrocarbons in biochar by using humic acid and oxalic acid. Background Art

[0002] Polycyclic aromatic hydrocarbons (PAHs) exist in soil in several different forms: free, organic-bound, and mineral-adsorbed. The free form refers to the form that exists independently, free from organic matter and minerals; the mineral-adsorbed form refers to adsorption on mineral surfaces; and the organic-bound form refers to a state in which PAHs are tightly bound to organic or colloidal particles in the soil, and are in dynamic equilibrium with the free form. As hydrophobic organic pollutants, PAHs primarily enter soil ecosystems by binding to organic matter and exist primarily in an organic-bound form.

[0003] Biochar is a solid product formed through thermochemical conversion under anaerobic conditions. It exhibits high stability, surface electrical conductivity, alkalinity, strong adsorption capacity, strong cation exchange capacity, a complex pore structure, and a large specific surface area. Biochar not only improves soil water and fertilizer retention, but also significantly improves soil aggregate structure and microbial community structure, and adsorbs and degrades heavy metals and pesticide residues in the soil. Previous studies have shown that the high-temperature pyrolysis of biomass produces polycyclic aromatic hydrocarbons (PAHs), which adhere to the surface and pores of biochar.

[0004] Endogenous polycyclic aromatic hydrocarbons (PAHs) in biochar can reduce soil microbial abundance, inhibit seed germination, reduce crop yields, and even cause plant death. Long-term biochar application can lead to increased soil pH, high ammonium concentrations, or excessive salinization, causing earthworm weight loss or even death. Organic pollutants in biochar can also enter the human body involved in biochar production and transportation through inhalation, skin contact, and dietary exposure, increasing cancer incidence. The degradation of PAHs is closely related to the number of benzene rings, molecular weight, and molecular structure. Low-molecular-weight PAHs have relatively simple molecular structures, high bioavailability, and are easily mineralized. Furthermore, low-ring PAHs, when applied to soil, undergo photolysis under sunlight, breaking down into harmless compounds. High-molecular-weight PAHs (4-6 rings) are generally more difficult to degrade than low-ring PAHs due to their more complex and stable molecular structures. Once released into the environment, high-ring PAHs can persist in soil and organisms for extended periods, accumulating and causing persistent harm to the environment and organisms. High-ring PAHs are generally more toxic and bioaccumulative. Their high lipid solubility in organisms makes them more likely to accumulate and accumulate in the food chain, exposing organisms at the top of the food chain (such as predators) to higher concentrations of toxic substances. Fluoranthene and chrysene, two typical tetracyclic aromatic hydrocarbons, are highly toxic and difficult to degrade.

[0005] Currently, PAHs soil remediation technologies include bioremediation, physical remediation, and chemical remediation. Bioremediation requires stringent conditions, making it difficult to control reaction conditions and maintain stable and continuous operation. Physical remediation merely transfers pollutants but does not degrade them. Chemical remediation primarily relies on photocatalytic oxidation, which requires specific catalysts and photocatalytic devices, resulting in high costs and inconvenient operation. Furthermore, these remediation technologies only target the removal of low-ring PAHs. Unlike free-state PAHs in soil, endogenous PAHs in soil biochar adhere to the biochar's surface and pores. Finding simpler methods to directly degrade them, particularly high-ring PAHs, remains a pressing technical challenge. Summary of the Invention

[0006] The present invention aims to provide a method and composition for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil. The method uses humic acid and oxalic acid to treat soil containing biochar, which can not only reduce the total content of endogenous PAHs in biochar, but also significantly promote the degradation of low-ring PAHs and high-ring PAHs, especially significantly improving the degradation rate of high-ring PAHs.

[0007] In a first aspect, the present invention provides a method for removing endogenous polycyclic aromatic hydrocarbons in biochar using humic acid and oxalic acid, comprising:

[0008] Humic acid and oxalic acid were added to the soil containing biochar to degrade endogenous polycyclic aromatic hydrocarbons in the biochar.

[0009] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid, the pH value of the biochar is 7 to 10, such as 7;

[0010] The specific surface area of the biochar is 3 to 20 m 2 / g, such as 3 m 2 / g;

[0011] The particle size of the biochar is ≤1 mm.

[0012] Specifically, the biochar is derived from crop straw, including at least one of corn straw, wheat straw, rice husk, and peanut shell. More specifically, the biochar can be obtained by continuous pyrolysis and carbonization of crop straw under an inert atmosphere, specifically by heating the temperature at 10°C / min to 500°C and maintaining the temperature for 2 hours.

[0013] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid, the mass percentage of the biochar in the soil is 5%.

[0014] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid, the mass ratio of the humic acid to the oxalic acid is 1000:1;

[0015] 1 g of the humic acid was added per 1 kg of soil.

[0016] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid, the humic acid includes fulvic acid, for example, 90% is fulvic acid.

[0017] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons in biochar by using humic acid and oxalic acid, in the treatment step, the particle size of the soil is controlled to be ≤2 mm;

[0018] In the treatment step, the water content of the soil is controlled to be 60% to 65% of the maximum water holding capacity, such as 60%;

[0019] In the treatment step, the temperature is 20 to 30°C;

[0020] The treatment time may specifically be 45 to 50 days, such as 50 days.

[0021] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid, the polycyclic aromatic hydrocarbons are 2-6 ring polycyclic aromatic hydrocarbons, including low-ring polycyclic aromatic hydrocarbons with 2-3 rings and high-ring polycyclic aromatic hydrocarbons with 4-6 rings. The low-ring polycyclic aromatic hydrocarbons can be at least one of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, and anthracene. The polycyclic aromatic hydrocarbons are high-ring polycyclic aromatic hydrocarbons with 4-6 rings, for example, at least one of fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]pyrene, and indeno[1,2,3-cd]pyrene. Preferably, the polycyclic aromatic hydrocarbons are 4-6 ring polycyclic aromatic hydrocarbons, more preferably 4-ring polycyclic aromatic hydrocarbons, such as fluoranthene or chrysene.

[0022] In a second aspect, the present invention provides a composition for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil, comprising humic acid and oxalic acid in a mass ratio of 1000:1.

[0023] In the above-mentioned composition for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil, the humic acid includes fulvic acid, for example, 90% is fulvic acid.

[0024] The present invention has the following beneficial effects:

[0025] 1. Adding oxalic acid and humic acid facilitates the degradation of endogenous PAHs in biochar in soil. The method not only reduces the total content of endogenous PAHs in biochar, but also significantly promotes the degradation of both low-ring and high-ring PAHs. In particular, it significantly increases the degradation rate of high-ring PAHs, with a particularly strong effect on fluoranthene and chrysene.

[0026] 2. Both organic acids and humic acid can promote the release of PAHs, increase the bioavailability of PAHs, and improve the activity of soil microorganisms.

[0027] 3. The test cycle is short, the effect is quick, the cost is low, and there is no secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The total PAHs content and degradation rate of different treatment groups in Example 1 and Comparative Examples 1-4 are shown.

[0029] Figure 2 The contents and degradation rates of low-ring PAHs (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene) in different treatment groups of Example 1 and Comparative Examples 1-4 are shown.

[0030] Figure 3The contents and degradation rates of high-ring PAHs (fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]pyrene, and indeno[1,2,3-cd]pyrene) in different treatment groups of Example 1 and Comparative Examples 1-4 are shown.

[0031] Figure 1-3 In the figure, the labels are as follows: BK-pure soil sample; BC-soil sample with 5% biochar added; OA-soil sample with 5% biochar and 1 mg / kg oxalic acid added; HA-soil sample with 5% biochar and 1 g / kg humic acid added; OAHA-soil sample with 5% biochar, 1 mg / kg oxalic acid, and 1 g / kg humic acid added. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0033] Unless otherwise specified, the methods used in the following examples are all conventional methods and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples are all commercially available unless otherwise specified.

[0034] The humic acid in the following examples is R011794 from Roan Reagent Company.

[0035] Example 1

[0036] This embodiment provides a method for degrading endogenous polycyclic aromatic hydrocarbons in soil using biochar. The method comprises preparing biochar and mixing the biochar with soil to simulate the treatment object indoors. Humic acid and oxalic acid are used as treatment reagents. A soil incubation test is conducted and the degradation effect is tested. The specific steps are as follows:

[0037] (1) Preparation of biochar: Select representative crop straw and rice husk and place them in a continuous pyrolysis carbonization furnace in a nitrogen atmosphere. Carbonize at 500 °C with a heating rate of 10 °C / min. After heating to the set temperature and keeping it warm for 2 h, the generated rice husk biochar is cooled to room temperature and crushed through a 1 mm sieve. The biochar under the sieve has a pH value of 7, which is neutral, and a specific surface area of 3 m 2 / g;

[0038] (2) Soil pretreatment: The soil was sieved through a 2 mm sieve to obtain the test soil. The biochar was mixed with the test soil at a mass ratio of 5%. Deionized water was added to keep the soil moisture at 60% of the maximum water holding capacity. The incubation room temperature was maintained at 25 ± 5 °C. During the incubation process, the soil was weighed and water was added every other day.

[0039] (3) Degradation treatment: The rice husk biochar was thoroughly mixed with the test soil and cultured. After 2 days, humic acid was added at 1 g / kg and oxalic acid was added at 1 mg / kg. Water was added every other day during the culture process. Destructive sampling was carried out at 0 days, 7 days, 14 days, 21 days and 50 days of culture. Multi-layer and multi-point sampling (mixture of soil and biochar) was carried out and stored in a cool place for air drying for the determination and analysis of PAHs content.

[0040] Comparative Example 1

[0041] Endogenous PAHs in biochar were removed from the soil according to the steps in Example 1, except that oxalic acid was added at 1 mg / kg in step (3) without adding humic acid. The remaining steps and conditions remained the same.

[0042] Comparative Example 2

[0043] Endogenous PAHs in biochar were removed from the soil according to the steps in Example 1, except that humic acid was added at 1 g / kg in step (3) without oxalic acid. The remaining steps and conditions remained the same.

[0044] Comparative Example 3

[0045] Endogenous PAHs in biochar from soil were removed according to the steps in Example 1, except that oxalic acid and humic acid were not added in step (3). The remaining steps and conditions remained the same.

[0046] Comparative Example 4

[0047] In the control group, the test soil was taken without any subsequent treatment.

[0048] Test Case

[0049] The content of polycyclic aromatic hydrocarbons in the samples of the above examples and comparative examples was determined as follows:

[0050] Total PAHs - Soxhlet extraction: The total amount of PAHs in biochar was extracted using accelerated solvent extraction, solid phase extraction cleanup, and gas chromatography-mass spectrometry determination.

[0051] (1) Solvent extraction: Accurately weigh a certain amount of air-dried, ground, and sieved sample (10 g of rice husk biochar, determined according to the sample concentration, can be extracted and then split), transfer it to a glass fiber filter cartridge, add 50 μL of PAHs purification standard, place the filter cartridge in a Soxhlet extractor, and extract continuously for 16 to 24 hours with 300 mL of a mixed solution of dichloromethane and acetone (1 / 1, V / V) at a reflux rate of not less than 4 times per hour.

[0052] (2) Sample concentration: After Soxhlet extraction, rotary evaporate to about 2 mL, add 20 mL of n-hexane and continue rotary evaporation to completely convert the solvent to n-hexane, and concentrate to less than 1 mL for purification; the dichloromethane extract after liquid-liquid extraction is rotary evaporated in the same way, the solvent is replaced with n-hexane, and concentrated to less than 1 mL for purification.

[0053] (3) Sample purification: A SUPELCO 24-tube cross-contamination-proof SPE device and a 500 mg / 6 mL silicycle SPE column were used to purify the sample. The SPE column was activated with 5 mL of a mixed solution of n-hexane and dichloromethane (85 / 15, V / V) and 10 mL (2 mL each time). The concentrated sample was transferred to the head of the SPE column and eluted with 5 mL of a mixed solution of n-hexane and dichloromethane (85 / 15, V / V). The flow rate of the sample and elution solvent should not be too fast or too slow, ensuring a flow rate of 1 drop / s. After the solvent was dried, the vacuum pump was turned on to dry the column.

[0054] (4) Nitrogen blowing and sample preparation: Blow the elution liquid nitrogen to 0.5 mL, add 50 μL of PAHs injection standard to the sample, vortex mix, transfer the sample into the sample bottle with a pipette, attach a label, and wait for testing.

[0055] The experimental results are as follows Figure 1-Figure 3 shown.

[0056] From the comparison results of Example 1 and Comparative Examples 1-4, it can be seen that the addition of oxalic acid and humic acid in the present invention is beneficial to the degradation of endogenous PAHs in biochar in soil. After 50 days of cultivation, the degradation rates of PAHs in Comparative Example 3, Comparative Example 1, Comparative Example 2, and Example 1 were 30.97%, 37.74%, 40.04%, and 52.27%, respectively. The degradation rates of low-ring PAHs were 39.98%, 49.18%, 49.67%, and 61.70%, respectively. The degradation rates of high-ring PAHs were 22.12%, 26.92%, 29.47%, and 41.82%, respectively. It can be seen that the addition of oxalic acid and humic acid are both beneficial to the degradation of endogenous PAHs in biochar in soil, among which the co-addition of oxalic acid and humic acid has the strongest degradation effect on endogenous PAHs in biochar. Polycyclic aromatic hydrocarbons involve 2-ring to 6-ring (including indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]pyrene, benzo[α]pyrene, benzo[k]fluoranthene, benzo[b]fluoranthene, chrysene, benzo[α]anthracene, pyrene, fluoranthene, anthracene, phenanthrene, fluorene, acenaphthene, acenaphthene and naphthalene).

[0057] Among them, the degradation rates of 4-6 ring PAHs by different treatment groups are shown in Tables 1-3. The numbers after each treatment group in Table 1 represent the number of culture days.

[0058] Table 1. Degradation rates of 4-ring and high-ring PAHs in different treatment groups

[0059]

[0060] Table 2. Degradation rates of 5-ring and high-ring PAHs in different treatment groups

[0061]

[0062] Table 3. Degradation rates of 6-ring PAHs in different treatment groups

[0063]

[0064] As shown in Tables 1-3, a comparison of the degradation rates of the different treatment groups after 50 days reveals that the degradation rates of the four rings, particularly fluoranthene and chrysene, were significantly increased. After 50 days, the degradation rate of fluoranthene in the BC treatment group was 37%, 47% with OA, 46% with HA, and 60% with OA + HA. After 50 days, the degradation rate of chrysene in the BC treatment group was 26%, 31% with OA, 24% with HA, and 42% with OA + HA.

[0065] It can be seen that the method of the present invention can not only remove the endogenous polycyclic aromatic hydrocarbons of biochar and degrade them in soil, but also has a significant promoting effect on the degradation of low-ring PAHs and high-ring PAHs, especially significantly improving the degradation rate of high-ring PAHs, and the degradation effect on fluoranthene and chrysene is particularly outstanding.

[0066] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, can implement the present invention in a wider range under equivalent parameters, concentration and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principle of the present invention, the application is intended to include any variation, purposes or improvements of the present invention, including departing from the disclosed scope in the application and the changes made with conventional techniques known in the art.

Claims

1. A method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid, characterized in that: The method comprises the following steps: adding humic acid and oxalic acid to soil containing biochar for treatment to degrade endogenous polycyclic aromatic hydrocarbons in the biochar; The mass percentage of the biochar in the soil is 5%; The mass ratio of the humic acid to the oxalic acid is 1000:1; 1 g of the humic acid was added per 1 kg of soil.

2. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 1, characterized in that: The pH value of the biochar is 7 to 10; The specific surface area of the biochar is 3 to 20 m 2 / g; The particle size of the biochar is ≤1 mm.

3. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 1, characterized in that: The humic acid includes fulvic acid.

4. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 1, characterized in that: In the treatment step, the particle size of the soil is controlled to be ≤2 mm; In the treatment step, the water content of the soil is controlled to be 60% to 65% of the maximum water holding capacity; In the treatment step, the temperature is 20 to 30°C; The treatment time is 45 to 50 days.

5. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 1, characterized in that: The polycyclic aromatic hydrocarbons are 2-6 ring polycyclic aromatic hydrocarbons.

6. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 5, characterized in that: The polycyclic aromatic hydrocarbons are 4-6 ring polycyclic aromatic hydrocarbons.

7. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 5, characterized in that: The polycyclic aromatic hydrocarbons are 4-ring polycyclic aromatic hydrocarbons.

8. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar using humic acid and oxalic acid according to claim 7, characterized in that: The four-ring polycyclic aromatic hydrocarbon is fluoranthene or

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