NANOBIOREMEDIATION METHOD FOR SOIL IN HIGH-CONCENTRATION POLYCYCLIC AROMATIC HYDROCARBON (PAH)-CONTAMINATED SITE

Abstract

A nanobioremediation method is for soil in a high-concentration polycyclic aromatic hydrocarbon (PAH)-contaminated site. The method includes adding a carbon nanomaterial and a base fertilizer to soil in a high-concentration PAH-contaminated site, evenly broadcast sowing alfalfa seeds to the contaminated soil, and keeping the soil moisture content at 60% of the field moisture capacity, and when the alfalfa grows to the flowering or maturity stage, harvesting and removing the plants from the contaminated soil.

Claims

1. A nanobioremediation method for soil in a high-concentration polycyclic aromatic hydrocarbon (PAH)-contaminated site, comprising the following steps: adding a carbon nanomaterial and a base fertilizer to soil in a high-concentration PAH-contaminated site; evenly broadcast sowing alfalfa seeds to the contaminated soil, and keeping the soil moisture content at 60% of the field moisture capacity; and when the alfalfa grows to the flowering or maturity stage, harvesting and removing the plants from the contaminated soil.

2. The nanobioremediation method for soil in a high-concentration PAH-contaminated site according to claim 1, wherein the carbon nanomaterial is at least one of single-walled carbon nanotube (SWCNT), multi-walled carbon nanotube (MWCNT) or sulfonated graphene.

3. The nanobioremediation method for soil in a high-concentration PAH-contaminated site according to claim 1, wherein the base fertilizer is urea, Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O and K.sub.2SO.sub.4.

4. The nanobioremediation method for soil in a high-concentration PAH-contaminated site according to claim 2, wherein the sulfonated graphene is added at an amount of 0.2 mg/g, the SWCNT is added at an amount of 0.05 mg/g, and the MWCNT is added at an amount 0.05 mg/g.

5. The nanobioremediation method for soil in a high-concentration PAH-contaminated site according to claim 3, wherein the base fertilizer is added at an amount as follows: 0.215 g of urea, 0.285 g of Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O and 0.188 g of K.sub.2SO.sub.4 per kilogram of soil.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 shows the effect of the dosage of sulfonated graphene on the PAH removal rate during the remediation of contaminated soil by alfalfa;

[0013] FIG. 2 shows the effect of the dosage of SWCNT on the PAH removal rate during the remediation of contaminated soil by alfalfa; and

[0014] FIG. 3 shows the effect of the dosage of MWCNT on the PAH removal rate during the remediation of contaminated soil by alfalfa.

DETAILED DESCRIPTION

[0015] The present invention will be further described below by way of examples, so as to clarify the outstanding features and significant progress of the present invention, which is merely to illustrate the present invention and is not limited to the following examples. The method of the present invention is adopted to remediate soil in a high-concentration PAH-contaminated site.

Example 1: Enhancing Effect of Sulfonated Graphene Added at Different Dosages on the Removal of PAHs in Soil by Alfalfa

[0016] The soil collected from a contaminated site of a coking plant in Nanjing was adopted as test soil for an indoor pot experiment. The collected soil was air-dried, then gravel and animal and plant residues therein were removed, and the resulting soil was sieved through a 4 mm sieve and mixed thoroughly. The PAH content in the soil was 344.48 mg/kg. 0.6 kg of soil was used for a pot, with 0.215 g of urea, 0.285 g of Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O and 0.188 g of K.sub.2SO.sub.4 per kilogram of soil. Sulfonated graphene was added to the soil, and different dosage levels (0.05, 0.1, 0.2, 0.5, 1.0 and 5.0 mg/g) were set, with 3 replicates for each dosage. The following method was adopted for the pregermination of alfalfa seeds: the alfalfa seeds were soaked in a 0.5% sodium hypochlorite solution for 10 min of surface sterilization, and then cleaned; the obtained alfalfa seeds were placed in a 95% alcohol solution for 10 min of surface sterilization, rinsed 5 times with sterile water, and then soaked in sterile water in a beaker for 2 h; and the soaked seeds were evenly placed in a sterile petri dish covered with a moist filter paper, and subjected to pregermination at 28° C. in the dark for 24 h. After the seeds had germinated, plump seeds with a fixed size were selected and spread evenly in the contaminated soil. 40 seeds were spread evenly in each pot, and after seedlings emerged, 30 seedlings with the same growth trend were selected and reserved. The potted plants were cultivated in a light cultivation room, with a temperature of about 26° C. during the day and a temperature of about 20° C. at night. The plants were watered regularly every day with deionized water to keep the soil moisture content at about 60% of the field moisture capacity. After alfalfa grew for 60 days, soil and plant samples were collected separately. The soil samples were lyophilized, ground, and sieved through a 100-mesh sieve, and the content of PAHs in the soil was determined by extraction. Moreover, a blank control without alfalfa being planted and a treatment group with alfalfa being planted alone were set up. In the blank control without alfalfa being planted, no sulfonated graphene was added, no alfalfa was planted, and the other conditions were the same as above. In the treatment group with alfalfa being planted alone, alfalfa was planted, but no sulfonated graphene was added, and the other conditions were the same as above. FIG. 1 shows the effect of the dosage of sulfonated graphene on the PAH removal rate during the remediation of contaminated soil by alfalfa.

[0017] As shown in FIG. 1, when sulfonated graphene is added at a relatively-low dosage, the PAH removal rate for the soil by alfalfa increases with increasing dosage of sulfonated graphene; when sulfonated graphene is added at 0.2 mg/g, alfalfa exhibits a maximum PAH removal rate for the soil, reaching 96.43%, which is much higher than that of the blank control without alfalfa being planted (42.71%) and the treatment group with alfalfa being planted alone (60.15%), indicating that sulfonated graphene exhibits an efficient enhancement effect on the PAH degradation by alfalfa rhizosphere; but as the dosage of sulfonated graphene is further increased, the PAH removal rate for the soil decreases, indicating that sulfonated graphene has an optimal dosage of 0.2 mg/g.

[0018] Table 1 shows the residual concentration of each component of PAHs in soil after the soil is remediated for 60 days by adding sulfonated graphene at 0.2 mg/g and planting alfalfa. It can be seen from the table that after remediation, the residual concentration of each component of PAHs in the soil is tremendously lower than the initial concentration, and are all below the contamination risk screening value for soil in construction land (first-class land), meeting the most stringent requirements for the redevelopment and reutilization of construction land; and in the blank control without alfalfa being planted and the treatment group with alfalfa being planted alone, the residual concentration of each component of PAHs is still relatively high, and most still far exceed the contamination risk screening value for soil in construction land (first-class land).

Example 2: Enhancing Effect of SWCNT Added at Different Dosages on the Removal of PAHs in Soil by Alfalfa

[0019] The soil collected from a contaminated site of a coking plant in Nanjing was adopted as test soil for an indoor pot experiment. The collected soil was air-dried, then gravel and animal and plant residues therein were removed, and the resulting soil was sieved through a 4 mm sieve and mixed thoroughly. The PAH content in the soil was 344.48 mg/kg. 0.6 kg of soil was used for a pot, with 0.215 g of urea, 0.285 g of Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O and 0.188 g of K.sub.2SO.sub.4 per kilogram of soil. SWCNT was added to the soil, and different dosage levels (0.05, 0.1, 0.2, 0.5, 1.0 and 5.0 mg/g) were set, with 3 replicates for each dosage. The following method was adopted for the forced germination of alfalfa seeds: the alfalfa seeds were soaked in a 0.5% sodium hypochlorite solution for 10 min of surface sterilization, and then cleaned; the obtained alfalfa seeds were placed in a 95% alcohol solution for 10 min of surface sterilization, rinsed 5 times with sterile water, and then soaked in sterile water in a beaker for 2 h; and the soaked seeds were evenly placed in a sterile petri dish covered with a moist filter paper, and subjected to forced germination at 28° C. in the dark for 24 h. After the seeds had germinated, plump seeds with a fixed size were selected and spread evenly in the contaminated soil. 40 seeds were spread evenly in each pot, and after seedlings emerged, 30 seedlings with the same growth trend were selected and reserved. The potted plants were cultivated in a light cultivation room, with a temperature of about 26° C. during the day and a temperature of about 20° C. at night. The plants were watered regularly every day with deionized water to keep the soil moisture content at about 60% of the field moisture capacity. After alfalfa grew for 60 days, soil and plant samples were collected separately. The soil samples were lyophilized, ground, and sieved through a 100-mesh sieve, and the content of PAHs in the soil was determined by extraction. Moreover, a blank control without alfalfa being planted and a control group with alfalfa being planted alone were set up. In the blank control without alfalfa being planted, no SWCNT was added, no alfalfa was planted, and the other conditions were the same as above. In the treatment group with alfalfa being planted alone, alfalfa was planted, but no SWCNT was added, and the other conditions were the same as above. FIG. 2 shows the effect of the dosage of SWCNT on the PAH removal rate during the remediation of contaminated soil by alfalfa.

[0020] As shown in FIG. 2, when SWCNT is added at 0.05 mg/g, alfalfa exhibits a maximum PAH removal rate for the soil, reaching 93.64%, which is much higher than that of the blank control without alfalfa being planted (42.71%) and the treatment group with alfalfa being planted alone (60.15%), indicating that SWCNT exhibits an efficient enhancement effect on the PAH degradation by alfalfa rhizosphere; as the dosage of SWCNT is increased, the PAH removal rate for the soil has no significant difference with that of the treatment group with alfalfa being planted alone; only when the dosage of SWCNT is increased to 1 mg/g, the PAH removal rate for the soil is increased by 13% compared with the treatment group with alfalfa being planted alone, but still significantly lower than that at the dosage of 0.05 mg/g, indicating that SWCNT has an optimal dosage of 0.05 mg/g.

[0021] Table 2 shows the residual concentration of each component of PAHs in soil after the soil is remediated for 60 days by adding SWCNT at 0.05 mg/g and planting alfalfa. It can be seen from the table that after remediation, the residual concentration of each component of PAHs in the soil is tremendously lower than the initial concentration, and except for benzo[a]pyrene, the other components all have a residual concentration below the contamination risk screening value for soil in construction land (first-class land), but benzo[a]pyrene also has a residual concentration lower than the risk control value for the first-class land; as alfalfa further grows, the concentration of benzo[a]pyrene will continue to decrease; and in the blank control without alfalfa being planted and the treatment group with alfalfa being planted alone, the residual concentration of each component of PAHs is still relatively high, and most still far exceed the contamination risk screening value for soil in construction land (first-class land).

Example 3: Enhancing Effect of MWCNT Added at Different Dosages on the Removal of PAHs in Soil by Alfalfa

[0022] The soil collected from a contaminated site of a coking plant in Nanjing was adopted as test soil for an indoor pot experiment. The collected soil was air-dried, then gravel and animal and plant residues therein were removed, and the resulting soil was sieved through a 4 mm sieve and mixed thoroughly. The PAH content in the soil was 344.48 mg/kg. 0.6 kg of soil was used for a pot, with 0.215 g of urea, 0.285 g of Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O and 0.188 g of K.sub.2SO.sub.4 per kilogram of soil. MWCNT was added to the soil, and different dosage levels (0.05, 0.1, 0.2, 0.5, 1.0 and 5.0 mg/g) were set, with 3 replicates for each dosage. The following method was adopted for the forced germination of alfalfa seeds: the alfalfa seeds were soaked in a 0.5% sodium hypochlorite solution for 10 min of surface sterilization, and then cleaned; the obtained alfalfa seeds were placed in a 95% alcohol solution for 10 min of surface sterilization, rinsed 5 times with sterile water, and then soaked in sterile water in a beaker for 2 h; and the soaked seeds were evenly placed in a sterile petri dish covered with a moist filter paper, and subjected to forced germination at 28° C. in the dark for 24 h. After the seeds had germinated, plump seeds with a fixed size were selected and spread evenly in the contaminated soil. 40 seeds were spread evenly in each pot, and after seedlings emerged, 30 seedlings with the same growth trend were selected and reserved. The potted plants were cultivated in a light cultivation room, with a temperature of about 26° C. during the day and a temperature of about 20° C. at night. The plants were watered regularly every day with deionized water to keep the soil moisture content at about 60% of the field moisture capacity. After alfalfa grew for 60 days, soil and plant samples were collected separately. The soil samples were lyophilized, ground, and sieved through a 100-mesh sieve, and the content of PAHs in the soil was determined by extraction. Moreover, a blank control without alfalfa being planted and a control group with alfalfa being planted alone were set up. In the blank control without alfalfa being planted, no MWCNT was added, no alfalfa was planted, and the other conditions were the same as above. In the treatment group with alfalfa being planted alone, alfalfa was planted, but no MWCNT was added, and the other conditions were the same as above. FIG. 3 shows the effect of the dosage of MWCNT on the PAH removal rate during the remediation of contaminated soil by alfalfa.

[0023] As shown in FIG. 3, when MWCNT is added at 0.05 mg/g to 0.2 mg/g, alfalfa exhibits a PAH removal rate of 99.05% to 99.98% for the soil, which is significantly higher than that of the treatment group with alfalfa being planted alone (60.15%) and much higher than that of the blank control without alfalfa being planted (42.71%), indicating that MWCNT exhibits an efficient enhancement effect on the PAH degradation by alfalfa rhizosphere; as the dosage of MWCNT is increased, the PAH removal rate for the soil has no significant difference with that of the treatment group with alfalfa being planted alone; but when the dosage of MWCNT is increased to 1 mg/g, the PAH removal rate for the soil is increased by 34% compared with the treatment group with alfalfa being planted alone; and given a comprehensive consideration including the MWCNT cost, it can be determined that MWCNT has an optimal dosage of 0.05 mg/g.

[0024] Table 3 shows the residual concentration of each component of PAHs in soil after the soil is remediated for 60 days by adding MWCNT at 0.05 mg/g and planting alfalfa. It can be seen from the table that after remediation, the residual concentration of each component of PAHs in the soil is tremendously lower than the initial concentration, and are all below the contamination risk screening value for soil in construction land (first-class land), meeting the most stringent requirements for the redevelopment and reutilization of construction land; and in the blank control without alfalfa being planted and the treatment group with alfalfa being planted alone, the residual concentration of each component of PAHs is still relatively high, and most still far exceed the contamination risk screening value for soil in construction land (first-class land).

TABLE-US-00001 TABLE 1 Enhancing effect of sulfonated graphene (SG) added at 0.2 mg/g on the removal of PAHs in soil by alfalfa Benzo Benzo Dibenzo [b] [k] Benzo [a, h] Benzo Phenan- Anthra- Fluoran- Benzo[a] fluoran- fluoran- [a] anthra- [g, h, i] Total Treatment Fluorene threne cene thene Pyrene anthracene Chrysene thene thene pyrene cene pyrene PAHs Initial 1.68 34.13 1.88 1.51 89.99 29.82 23.44 25.86 13.64 33.32 2.12 27.09 344.48 concentration in soil The control 0.28 14.23 0.45 33.14 57.28 18.14 14.66 14.37 7.22 21.42 0.98 15.17 197.34 with no plants Planting 0.15 12.91 0.26 21.93 41.44 12.96 7.82 9.86 4.23 15.36 0.33 10.05 137.28 alfalfa alone Adding SG 0.04 0.72 0.15 2.52 3.36 0.85 0.67 2.05 0.44 0.47 0.41 0.77 12.31 (0.2 mg/g) + planting alfalfa Contamination 5.5 490 5.5 55 0.55 0.55 risk screening value for soil in construction land (first- class land) indicates data missing or illegible when filed

TABLE-US-00002 TABLE 2 Enhancing effect of SWCNT added at 0.05 mg/g on the removal of PAHs in soil by alfalfa Benzo Benzo Dibenzo [b] [k] Benzo [a, h] Benzo Phenan- Anthra- Fluoran- Benzo[a] fluoran- fluoran- [a] anthra- [g, h, i] Total Treatment Fluorene threne cene thene Pyrene anthracene Chrysene thene thene pyrene cene pyrene PAHs Initial 1.68 34.13 1.88 1.51 89.99 29.82 23.44 25.86 13.64 33.32 2.12 27.09 344.48 concentration in soil The control 0.28 14.23 0.45 33.14 7.28 18.14 14.66 14.37 7.22 21.42 0.98 15.17 197.34 with no plants Planting 0.15 12.91 0.26 21.93 41.44 12.9  7.82 9.8  4.23 1  .3  0.33 10.05 137.28 alfalfa alone Adding 0.10 1.92 0.19 4.58 5.61 1.99 1.65 2.10 0.99 1.98 0.12 1.26 22.50 SWCNT (0.05 mg/g) + planting alfalfa Contamination 5.5 490 5.5 55 0.55 0.55 risk screening value for soil in construction land (first- class land) indicates data missing or illegible when filed

TABLE-US-00003 TABLE 3 Enhancement effect of MWCNT added at 0.05 mg/g on the removal of PAHs in soil by alfalfa Benzo Benzo Dibenzo [b] [k] Benzo [a, h] Benzo Phenan- Anthra- Fluoran- Benzo[a] fluoran- fluoran- [a] anthra- [g, h, i] Total Treatment Fluorene threne cene thene Pyrene anthracene Chrysene thene thene pyrene cene pyrene PAHs Initial 1.68 34.13 1.88 1.51 89.99 29.82 23.44 25.86 13.64 33.32 2.12 27.09 344.48 concentration in soil The control 0.28 14.23 0.45 33.14 57.28 18.14 14.  14.37 7.22 21.42 0.98 15.17 197.34 with no plants Planting 0.15 12.91 0.26 21.93 41.44 12.96 7.82 9.86 4.23 15.36 0.33 10.05 137.28 alfalfa alone Adding 0.01 0.18 0.00 0.27 0.85 0.31 0.29 0.18 0.09 0.23 0.04 0.85 3.29 MWCNT (0.05 mg/g) + planting alfalfa Contamination 5.5 490 5.5 55 0.55 0.55 risk screening value for soil in construction land (first- class land) indicates data missing or illegible when filed