Method and composition for removing endogenous polycyclic aromatic hydrocarbon in biochar by humic acid and oxalic acid

Abstract

The invention discloses a method and a composition for removing endogenous polycyclic aromatic hydrocarbon in biochar by humic acid and oxalic acid. The method for removing the biochar endogenous polycyclic aromatic hydrocarbon by using the humic acid and the oxalic acid comprises the following steps: adding the humic acid and the oxalic acid into soil containing biochar for treatment so as to degrade the biochar endogenous polycyclic aromatic hydrocarbon. The method disclosed by the invention not only can reduce the total content of endogenous PAHs of the biochar, but also has a relatively remarkable promotion effect on low-ring PAHs and high-ring PAHs, especially can remarkably improve the degradation rate of high-ring PAHs, and has a particularly outstanding degradation effect on fluoranthene and fluoranthene.

Description

Technical Field

[0001] The 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, including free form, organic matter-bound form, and mineral adsorption form. The free form refers to the form that exists independently from organic matter and minerals, the mineral surface adsorption state refers to the adsorption on the surface of minerals, and the organic matter-bound state refers to a state that is tightly bound to organic matter particles or colloidal particles in the soil, and is in a dynamic equilibrium with free-state PAHs. PAHs, as hydrophobic organic pollutants, mainly enter the soil ecosystem by combining with organic matter, and mainly exist in an organic matter-bound state.

[0003] Biochar refers to a solid product formed by thermochemical transformation under anaerobic conditions. It has the characteristics of high stability, surface electrical properties, alkalinity, strong adsorption capacity, strong cation exchange capacity, complex pore structure, and large specific surface area. Biochar can not only improve the water and fertilizer retention properties of the soil, but also has significant effects in improving the soil's aggregate structure, microbial community structure, and adsorbing and passivating heavy metals and pesticide residues in the soil. Studies have shown that polycyclic aromatic hydrocarbons will be produced during the high-temperature pyrolysis of biomass, and will adhere to the surface and pores of biochar.

[0004] Endogenous PAHs in biochar can reduce the abundance of soil microorganisms, inhibit seed germination, reduce crop yields, and even cause plant death. Long-term application of biochar may lead to increased soil pH, high-concentration ammonium or excessive salinization, causing earthworm weight loss or even death. Organic pollutants in biochar may also enter the human body engaged in the production and transportation of biochar through inhalation, skin contact and dietary exposure, thereby increasing the incidence of cancer. The degradation of PAHs is closely related to the number of benzene rings, molecular weight and molecular structure. Low molecular weight PAHs have a relatively simple molecular structure, high bioavailability, and are easily mineralized. After low-ring PAHs are applied to the soil, they will undergo photolysis under sunlight and decompose into harmless compounds. High molecular weight PAHs with 4-6 rings are usually more difficult to degrade than low-ring PAHs because their molecular structure is more complex and stable. Once released into the environment, high-ring PAHs may exist in the soil and organisms for a long time, accumulating for a long time and causing continuous harm to the environment and organisms. In addition, high-ring PAHs usually have stronger biological toxicity and bioaccumulation. They are highly fat-soluble in organisms and are more likely to be enriched and accumulated in the food chain, causing organisms at the top of the food chain (such as predators) to be exposed to higher concentrations of toxic substances. Among them, fluoranthene and chrysene, as two typical tetracyclic aromatic hydrocarbons, are highly toxic and difficult to degrade.

[0005] At present, PAHs soil remediation technologies include bioremediation, physical remediation and chemical remediation. On the one hand, bioremediation conditions are harsh, reaction conditions are difficult to control, and it is difficult to operate stably and continuously. Physical remediation only transfers pollutants but does not achieve degradation. Chemical remediation mainly uses photocatalytic oxidation, which requires the use of specific catalysts and photocatalytic devices, which is costly and inconvenient to operate. On the other hand, the above remediation technologies are still only aimed at the removal of low-ring PAHs. Different from free PAHs in soil, endogenous PAHs in biochar in soil are attached to the surface and pores of biochar. How to directly degrade them by simpler means, especially the degradation of high-ring PAHs, is still a technical problem that needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is 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 has a significant promoting effect on the degradation of low-ring PAHs and high-ring PAHs, especially can significantly improve 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 by using humic acid and oxalic acid, comprising: Humic acid and oxalic acid were added to the soil containing biochar for treatment to degrade endogenous polycyclic aromatic hydrocarbons in the biochar.

[0008] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid, the pH value of the biochar is 7 to 10, such as 7; The specific surface area of ​​the biochar is 3 to 20 m 2 / g, such as 3 m 2 / g; The particle size of the biochar is ≤1 mm.

[0009] Specifically, the biochar is 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 at 10°C / min to 500°C and keeping the temperature for 2 hours.

[0010] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid, the mass percentage of the biochar in the soil is 5%.

[0011] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid, 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.

[0012] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid, the humic acid includes fulvic acid, such as 90% fulvic acid.

[0013] In the above-mentioned method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid, 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, such as 60%; In the treatment step, the temperature is 20 to 30°C; The treatment time may specifically be 45 to 50 days, such as 50 days.

[0014] In the above-mentioned method of removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid, the polycyclic aromatic hydrocarbons are 2-6 ring polycyclic aromatic hydrocarbons, including 2-3 ring low-ring polycyclic aromatic hydrocarbons and 4-6 ring high-ring polycyclic aromatic hydrocarbons. Among them, the low-ring polycyclic aromatic hydrocarbons can be at least one of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, and anthracene. The polycyclic aromatic hydrocarbons are 4-6 ring high-ring polycyclic aromatic hydrocarbons, for example, they can be 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.

[0015] 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.

[0016] In the above-mentioned composition for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil, the humic acid includes fulvic acid, such as 90% fulvic acid.

[0017] The present invention has the following beneficial effects: 1. Adding oxalic acid and humic acid is beneficial to the degradation of endogenous PAHs in biochar in soil. The method of the present invention can not only reduce the total content of endogenous PAHs in biochar, but also has a significant promoting effect on both low-ring and high-ring PAHs, especially significantly improving the degradation rate of high-ring PAHs, and the degradation effect on fluoranthene and chrysene is particularly prominent.

[0018] 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.

[0019] 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

[0020] Figure 1 The total PAHs content and degradation rate of different treatment groups in Example 1 and Comparative Examples 1-4.

[0021] 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.

[0022] Figure 3 The 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.

[0023] Figure 1-3 In the figure, the labels are as follows: BK-pure soil sample; BC-soil sample with 5% biochar added; OA-sample with 5% biochar and 1 mg / kg oxalic acid added; HA-sample with 5% biochar and 1 g / kg humic acid added; OAHA-sample with 5% biochar, 1 mg / kg oxalic acid, and 1 g / kg humic acid added. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0025] The methods used in the following examples, unless otherwise specified, are all conventional methods, carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0026] The humic acid in the following examples is R011794 from Roan's Reagent Company.

[0027] Example 1 This embodiment provides a method for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil, by preparing biochar and mixing the biochar with soil to simulate the treatment object indoors, using humic acid and oxalic acid as treatment reagents, conducting soil cultivation tests and testing the degradation effect thereof, and the specific steps are as follows: (1) Preparation of biochar: Representative crop straw and rice husk were selected and placed in a continuous pyrolysis carbonization furnace. The carbonization temperature was 500 °C in a nitrogen atmosphere with a heating rate of 10 °C / min. The temperature was heated to the set temperature and then kept at this temperature for 2 h. The generated rice husk biochar was then cooled to room temperature and crushed through a 1 mm sieve. The biochar under the sieve was collected. The pH value of the biochar was 7, which was neutral, and the specific surface area was 3 m 2 / g; (2) Soil pretreatment: The soil was sieved through a 2 mm sieve to obtain the test soil. The biochar and test soil were mixed at a 5% (mass ratio). Deionized water was added to keep the soil moisture at 60% of the maximum water holding capacity. The temperature of the culture room was maintained at 25 ± 5 °C. During the culture process, the soil was weighed and the water was replenished every other day. (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, respectively. During the culture process, water was weighed and replenished every other day. Destructive sampling was carried out at 0, 7, 14, 21 and 50 days of culture. Multi-layer and multi-point sampling (mixture of soil and biochar) was carried out and placed in a cool place to air-dry for the determination and analysis of PAHs content.

[0028] Comparative Example 1 The steps in Example 1 were followed to remove endogenous PAHs from biochar in soil, except that 1 mg / kg oxalic acid was added in step (3) without adding humic acid. The remaining steps and conditions remained the same.

[0029] Comparative Example 2 The steps in Example 1 were followed to remove endogenous PAHs from biochar in soil, except that humic acid was added at 1 g / kg in step (3) without adding oxalic acid. The remaining steps and conditions remained the same.

[0030] Comparative Example 3 The steps in Example 1 were followed to remove endogenous PAHs from biochar in soil, except that oxalic acid and humic acid were not added in step (3). The remaining steps and conditions remained the same.

[0031] Comparative Example 4 In the control group, the test soil was taken without any subsequent treatment.

[0032] Test Case The content of polycyclic aromatic hydrocarbons in the samples in the above examples and comparative examples was determined in the following steps: Total PAHs-Soxhlet extraction: The total amount of PAHs in biochar was extracted using accelerated solvent extraction, solid phase extraction purification, and gas chromatography-mass spectrometry determination.

[0033] (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 h 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.

[0034] (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. Rotary evaporate the dichloromethane extract after liquid-liquid extraction in the same way, replace the solvent with n-hexane, and concentrate to less than 1 mL for purification.

[0035] (3) Sample purification: Use SUPELCO 24-tube cross-contamination-proof SPE device and 500 mg / 6 mL silicycle SPE column 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 SPE column head 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, and the flow rate should be 1 drop / s. After the solvent has dried up, turn on the vacuum pump to dry the column.

[0036] (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 a sample bottle with a pipette, attach a label, and wait for testing.

[0037] The experimental results are as follows Figure 1-Figure 3 shown.

[0038] 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 the 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, and 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 is beneficial to the degradation of endogenous PAHs in biochar in the soil, among which the co-addition of oxalic acid and humic acid has the strongest degradation effect on endogenous PAHs in biochar. PAHs involve 2-6 rings (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).

[0039] Among them, the degradation rates of 4-6-ring high-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.

[0040] Table 1. Degradation rates of 4-ring PAHs in different treatment groups

[0041] Table 2. Degradation rates of 5-ring PAHs in different treatment groups

[0042] Table 3. Degradation rates of 6-ring PAHs in different treatment groups

[0043] As can be seen from Tables 1-3, by comparing the degradation rates of different treatment groups after 50 days, it was found that the degradation rates of 4-ring, especially fluoranthene and chrysene, were significantly improved. After 50 days, the degradation rate of fluoranthene in the BC treatment group was 37%, 47% after adding OA, 46% after adding HA, and 60% after adding OA+HA. After 50 days, the degradation rate of chrysene in the BC treatment group was 26%, 31% after adding OA, 24% after adding HA, and 42% after adding OA+HA.

[0044] 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 the soil, but also has a significant promoting effect on the degradation of low-ring PAHs and high-ring PAHs, especially it can significantly improve the degradation rate of high-ring PAHs, and the degradation effect on fluoranthene and chrysene is particularly prominent.

[0045] 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, concentrations 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 changes, uses or improvements to 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 by 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 so as to degrade endogenous polycyclic aromatic hydrocarbons in the biochar.

2. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar by 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 by using humic acid and oxalic acid according to claim 1, characterized in that: The mass percentage of the biochar in the soil is 5%.

4. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid according to claim 1, characterized in that: The mass ratio of the humic acid to the oxalic acid is 1000:1; Add 1g of the humic acid per 1kg of soil; The humic acid includes fulvic acid.

5. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar by 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.

6. The method for removing endogenous polycyclic aromatic hydrocarbons from biochar by using humic acid and oxalic acid according to claim 1, characterized in that: The polycyclic aromatic hydrocarbons are 2-6 ring polycyclic aromatic hydrocarbons, preferably 4-6 ring polycyclic aromatic hydrocarbons.

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

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

9. A composition for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil, characterized in that: It includes humic acid and oxalic acid in a mass ratio of 1000:

1.

10. The composition for degrading endogenous polycyclic aromatic hydrocarbons in biochar in soil according to claim 9, characterized in that: The humic acid includes fulvic acid.

Images