High Molecular Weight Polycyclic Aromatic Hydrocarbons Removal Research Articles

Response of soil bacterial communities to polycyclic aromatic hydrocarbons during the phyto-microbial remediation of a contaminated soil

Rhizo-box experiments were conducted to analyze the phyto-microbial remediation potential of a grass (Lolium multiflorum L.) and a crop (Glycine max L.) combined with exogenous strain (Pseudomonas sp.) for polycyclic aromatic hydrocarbons (PAHs) contaminated soils. The dynamics of bacterial community composition, abundances of 16 S rDNA and ring hydroxylating dioxygenases (RHDα) genes, and removal of PAHs were evaluated and compared on four culture stages (days 0, 10, 20, and 30). The results showed that 8.65%–47.42% of Σ12 PAHs were removed after 30 days of cultivation. Quantitative polymerase chain reaction (qPCR) analysis indicated that treatments with soybean and ryegrass rhizosphere markedly increased the abundances of total bacteria and PAH-degraders, especially facilitated the growth of gram-negative degrading bacteria. Flavobacterium sp. and Pseudomonas sp. were the main and active strains in the control soil. However, the presence of plants and/or exogenous Pseudomonas sp. changed the soil bacterial community structure and modified the bacterial diversity of PAH-degraders. On the whole, this study showed that the high molecular weight PAHs removal efficiency of phyto-microbial remediation with ryegrass was better than those of remediation with soybean. Furthermore, the removals of PAHs strongly coincided with the abundance of PAH-degraders and bacterial community structure.

The role of lipopeptide biosurfactant on microbial remediation of aged polycyclic aromatic hydrocarbons (PAHs)-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) have been recognised as priority pollutants due to their carcinogenic, mutagenic and teratogenic properties. Bioremediation of PAHs is limited by low bioavailability of soil-bound PAHs due to their low aqueous solubility, high hydrophobicity and strong sorption to soil. The purpose of this study was to investigate the biodegradation enhancement potential of a heavy molecular mass lipopeptidal biosurfactant produced by Bacillus cereus SPL-4 on an aged wood treatment plant soil heavily contaminated with PAHs. In the laboratory scale batch treatments conducted (concentration of 6745.5mgkg−1, sum of 13PAHs) the high molecular weight PAHs removal rate was significantly enhanced in the biosurfactant supplemented microcosms than in the surfactant free controls. In the microcosms supplemented with 0.2 and 0.6% (w/w) lipopeptide, 51.2% of 4-ring and 55% of 5- and 6-ring PAHs; 64.1% of 4-ring and 79% of 5- and 6-ring PAHs were removed respectively, compared to 29% of 4-ring and 25.5% of 5- and 6-ring PAHs removal in the surfactant free control after 64daysof incubation. However, there was no statistically significant change in the degradation rates of low molecular weight PAHs in surfactant amended and surfactant free controls. Fitting the experimental data to two compartment model showed that the biosurfactant addition at 0.2 and 0.6% (w/w) increased the fast degradation fraction to 34.2 and 63% respectively, compared to 6% at the surfactant free controls. The degradation of 5 and 6 ring PAHs was significantly enhanced (p<0.05) in the higher surfactant dosage compared to the lower dosage. The results suggest that biosurfactant assisted degradation by microbial consortium may be a promising practical bioremediation strategy for aged PAH-contaminated soils.

Improving Polycyclic Aromatic Hydrocarbon Biodegradation in Contaminated Soil Through Low-Level Surfactant Addition After Conventional Bioremediation

Efficacy of bioremediation for soil contaminated with polycyclic aromatic hydrocarbons (PAHs) may be limited by the fractions of soil-bound PAHs that are less accessible to PAH-degrading microorganisms. In previous test-tube-scale work, submicellar doses of nonionic surfactants were screened for their ability to enhance the desorption and biodegradation of residual PAHs in soil after conventional bioremediation in a laboratory-scale, slurry-phase bioreactor. Polyoxyethylene sorbitol hexaoleate (POESH) was the optimum surfactant for enhancing PAH removal, especially the high-molecular weight PAHs. This work extends that concept by treating the effluent from the slurry-phase bioreactor in a second-stage batch reactor, to which POESH was added, for an additional 7 or 12 days. Surfactant amendment removed substantial amounts of the PAHs and oxy-PAHs remaining after conventional slurry-phase bioremediation, including more than 80% of residual 4-ring PAHs. Surfactant-amended treatment decreased soil cytotoxicity, but often increased the genotoxicity of the soil as measured using the DT-40 chicken lymphocyte DNA damage response assay. Potential ecotoxicity, measured using a seed germination assay, was reduced by bioreactor treatment and was reduced further after second-stage treatment with POESH. Of bacteria previously implicated as potential PAH degraders under POESH-amended conditions in a prior study, members of the Terrimonas genus were associated with differences in high-molecular weight PAH removal in the current study. Research using submicellar doses of surfactant as a second-stage treatment step is limited and these findings can inform the design of bioremediation systems at field sites treating soil contaminated with PAHs and other hydrophobic contaminants that have low bioaccessibility.

631 National assessment of long-term use of paraquat for its food and environmental-safety in Korea

Polycyclic aromatic hydrocarbons (PAHs) have been recognised as priority pollutants due to their carcinogenic, mutagenic and teratogenic properties. Bioremediation of PAHs is limited by low bioavailability of soil-bound PAHs due to their low aqueous solubility, high hydrophobicity and strong sorption to soil. The purpose of this study was to investigate the biodegradation enhancement potential of a heavy molecular mass lipopeptidal biosurfactant produced by Bacillus cereus SPL-4 on an aged wood treatment plant soil heavily contaminated with PAHs. In the laboratory scale batch treatments conducted (concentration of 6745.5 mg kg−1, sum of 13 PAHs) the high molecular weight PAHs removal rate was significantly enhanced in the biosurfactant supplemented microcosms than in the surfactant free controls. In the microcosms supplemented with 0.2 and 0.6% (w/w) lipopeptide, 51.2% of 4-ring and 55% of 5- and 6-ring PAHs; 64.1% of 4-ring and 79% of 5- and 6-ring PAHs were removed respectively, compared to 29% of 4-ring and 25.5% of 5- and 6-ring PAHs removal in the surfactant free control after 64 days of incubation. However, there was no statistically significant change in the degradation rates of low molecular weight PAHs in surfactant amended and surfactant free controls. Fitting the experimental data to two compartment model showed that the biosurfactant addition at 0.2 and 0.6% (w/w) increased the fast degradation fraction to 34.2 and 63% respectively, compared to 6% at the surfactant free controls. The degradation of 5 and 6 ring PAHs was significantly enhanced (p < 0.05) in the higher surfactant dosage compared to the lower dosage. The results suggest that biosurfactant assisted degradation by microbial consortium may be a promising practical bioremediation strategy for aged PAH-contaminated soils.