Influence of hydroxypropyl-β-cyclodextrin on the biodegradation of C-phenanthrene and C-hexadecane in soil

Soil was spiked with [9-¹⁴C]phenanthrene and [1-¹⁴C]hexadecane at 50 mg kg⁻¹ and aged for 1, 25, 50, 100 and 250 d. At each time point, the microcosms were amended with aqueous solutions of cyclodextrin (HP-β-CD) at a range of concentrations (0-40 mM). Mineralisation assays and aqueous HP-β-CD extractions were performed to assess the effect of the amendments on microbial degradation. The results showed that amendments had no significant impact on the microbial degradation of either of the ¹⁴C-contaminants. Further, HP-β-CD extractions were correlated with the mineralisation of the target chemicals in each of the soil conditions. It was found that the HP-β-CD extraction was able to predict mineralisation in soils which had not been amended with cyclodextrin; however, in the soils containing the HP-β-CD, there was no predictive relationship. Under the conditions of this study, the introduction of HP-β-CD into soils did not enhance the biodegradation of the organic contaminants.     

Environmentally friendly assessment of organic compound bioaccessibility using sub-critical water

The evaluation of microbial availability of contaminants is of high importance for better reflecting the processes governing contaminant fate in soil and for establishing the risk associated with contaminated sites. A sub-critical water extraction technique was assessed for its potential to determine the microbially degradable fraction of [¹⁴C]phenanthrene-associated activity in two dissimilar soils at three different ageing times (14, 28 and 49 days). For the majority of determinations, no significant (p > 0.05) difference between sub-critical water-extracted ¹⁴C-activity at 160 °C and the fraction mineralized by catabolically active Pseudomonas sp. was observed. Collectively, the results suggested that the sub-critical water extraction technique was an appropriate technique for predicting the biodegradable fraction of phenanthrene-associated ¹⁴C-activity in dissimilar soils following increasing soil-contaminant contact time.     

Electrochemical remediation of phenanthrene from contaminated kaolinite

In this work a two-stage process combining soil electrokinetic remediation and liquid electrochemical oxidation for the remediation of polluted soil with organic compounds has been developed and evaluated using phenanthrene-spiked kaolinite. Application of an unenhanced electrokinetic process resulted in negligible removal of phenanthrene from the kaolinite sample. Addition of co-solvents and electrolyte to the processing fluid used in the electrode chambers enhanced phenanthrene desorption from the kaolinite matrix and favoured electro-osmotic flow. Near-complete removal of phenanthrene was achieved using Na₂SO₄ and ethanol in the processing fluid. Phenanthrene was transported towards the cathode chamber where it was collected. The cathodic solution containing the pollutant was treated by electrochemical oxidation; complete degradation of phenanthrene occurred after 9 h using Na₂SO₄ as electrolyte.     

Effects of humic acid coatings on phenanthrene sorption to black carbon

Black carbon (BC) can strongly adsorb hydrophobic organic compounds (HOCs).The HOC sorption to coated BC could be attenuated in soil and sediment compared with that of the parent BC.To study the potential causes of the sorption attenuation,humic acid (HA) and BC were isolated.Phenanthrene (PHE) was selected as the representative of HOCs.BC was coated with the precipitated HA.The PHE sorption to the HA-coated BC was determined.The HA coatings on BC could result in the significant sorption attenuation of PHE to BC.The attenuation varied in different HA origin and was positively correlated to the aromaticity of HA.The attenuation could be explained by the direct competition between HA and PHE for the available sorption sites on BC and the reduction of the available sorption sites as a result of the pore blockage of BC caused by the HA coatings.Therefore,the HA coatings on BC was one potential cause of the attenuation of HOC sorption to BC in soil and sediment.     

Sorption of phenanthrene to biochar modified by base

Biochar (BC) is a potential material for removal of polycyclic aromatic hydrocarbons from soil and water, and base modification is a promising method for improving its sorption ability. In this study, we synthesized a series of base-modified biochars, and evaluated their sorption of phenanthrene. Original biochars were produced by pyrolysis of three feedstocks (rice straw, wood and bamboo) at five temperatures (300°C, 350°C, 400°C, 500°C and 700°C). Base-modified biochars were further obtained by washing of biochars with base solution. The base soluble carbon (SC) was extracted from the supernatant, which were only obtained from biochars pyrolyzed at low temperatures (<500°C) and the content was decreased with the increase of pyrolysis temperature. The SC content between different feedstocks followed the trend of rice straw>wood>bamboo when same pyrolysis conditions were applied. It was found that base modification improved the sorption of phenanthrene on biochars that SC could be extracted from (extractable-BCs). However, base treatment but had limited effects for biochars that no SC could be extracted from. It suggested that base modification improved the sorption of phenanthrene to extractable-BCs by removing the SC and thus increasing the surface area and hydrophobicity. Therefore, base modification was suggested to be used in modifying extractable-BCs.

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Phenanthrene uptake by Medicago sativa L. under the influence of an arbuscular mycorrhizal fungus

Phenanthrene uptake by Medicago sativa L. was investigated under the influence of an arbuscular mycorrhizal fungus. Inoculation of lucerne with the arbuscular mycorrhizal fungus Glomus etunicatum L. resulted in higher phenanthrene accumulation in the roots and lower accumulation in the shoots compared to non-mycorrhizal controls. Studies on sorption and desorption of phenanthrene by roots and characterization of heterogeneity of mycorrhizal and non-mycorrhizal roots using solid-state ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) demonstrated that increased aromatic components due to mycorrhizal inoculation resulted in enhanced phenanthrene uptake by the roots but lower translocation to the shoots. Direct visualization using two-photon excitation microscopy (TPEM) revealed higher phenanthrene accumulation in epidermal cells of roots and lower transport into the root interior and stem in mycorrhizal plants than in non-mycorrhizal controls. These results provide some insight into the mechanisms by which arbuscular mycorrhizal inoculation may influence the uptake of organic contaminants by plants.     

The effects of aging time on the fraction distribution and bioavailability of PAH

Understanding the effects of aging time on the fraction distribution and bioavailability of PAH, such as phenanthrene (PHE) and pyrene (PYR), has considerable benefits for risk assessment, food security and remediation strategies for contaminated soil. The results of the present study show that the proportion of the desorbed PHE decreased from ca. 82% at day 0 to ca. 65% at day 150. In addition, non-desorbed PHE increased from ca. 18% at day 0 to ca. 31% at day 150, whereas the changes of desorbed and non-desorbed PYR showed no significant trend during this aging period. The proportion of desorbed PYR was lower than that of PHE, whereas the opposite occurred with the non-desorbed fraction. After 150 d of aging, the proportion of bound residues (PHE and PYR) increased significantly with the cultivating time from ca. 0.2% to ca. 4.7% and ca. 0.1% to ca. 1.2% for PHE and PYR, respectively. In addition, the bioavailability of PAH (PHE and PYR) to earthworms was also assessed over 0-150 d. The results showed that the uptake rate and bioconcentration factor (BCF) of pollutants by earthworms displayed the following biphasic character: a rapid decrease over the first 15 d followed by a slow decrease over the next 135 d. Moreover, the earthworm uptake rate of PHE was greater than that of PYR throughout the incubation period, indicating that PHE has a higher bioavailability than PYR. In addition, the positive correlation between the uptake rate of earthworms and PAH extractability suggested that a three-step extraction is a reliable approach to predict PHE bioavailability in soil. However, a limit was observed for PYR.     

Characterization of a phenanthrene-degrading methanogenic community

Polycyclic aromatic hydrocarbons (PAHs) often occur in oil-contaminated soil, coke wastewater and domestic sludge; however, associated PAH degraders in these environments are not clear. Here we evaluated phenanthrene degradation potential in the mixed samples of above environments, and obtained a methanogenic community with different microbial profile compared to those from sediments. Phenanthrene was efficiently degraded (1.26 mg/L/d) and nonstoichiometric amount of methane was produced simultaneously. 16S rRNA gene sequencing demonstrated that bacterial populations were mainly associated with Comamonadaceae Nocardiaceae and Thermodesulfobiaceae, and that methanogenic archaea groups were dominated by Methanobacterium and Methanothermobacter. Substances such as hexane, hexadecane, benzene and glucose showed the most positive effects on phenanthrene degradation. Substrate utilization tests indicated that this culture could not utilize other PAHs. These analyses could offer us some suggestions on the putative phenanthrene-degrading microbes in such environments, and might help us develop strategies for the removal of PAHs from contaminated soil and sludge.

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Efficacy of in-situ for the remediation of PAH contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are of environmental concern because many PAHs are either carcinogens or potential carcinogens. Petroleum products are a major source of PAHs. The occurrence of PAH contamination is widespread and novel treatment technologies for the remediation of contaminated soils are necessary.Ozone has been found to be extremely useful for the degradation of PAHs in soils. For these compounds, the reaction with molecular ozone appears to be the more important degradation pathway. Greater than 95% removal of phenanthrene was achieved with an ozonation time of 2.3 h at an ozone flux of 250 mg h⁻¹. After 4.0 h of treatment at an ozone flux of 600 mg h⁻¹, 91 % of the pyrene was removed. We have also found that the more hydrophobic PAHs (e.g. chrysene) react more slowly than would be expected on the basis of their reactivity with ozone, suggesting that partitioning of the contaminant into soil organic matter may reduce the reactivity of the compound. Even so, after 4 h of exposure to ozone, the chrysene concentration in a contaminated Metea soil was reduced from 100 to 50 mg kg⁻¹ .Ozone has been found to be readily transported through columns packed with a number of geological materials, including Ottawa sand, Metea soil, Borden aquifer material and Wurtsmith aquifer material. All of these geological materials exerted a limited (finite) ozone demand, i.e. the rate of ozone degradation in soil columns is very slow after the ozone demand is met. Moisture content was found to increase the ozone demand, most likely owing to the dissolution of gaseous ozone into the pore water. As once the initial ozone demand is met, little degradation of ozone is observed, it should be possible to achieve ozone penetration to a considerable distance away from the injection well, suggesting that in-situ ozonation is a feasible means of treating uncontaminated unsaturated soils. This is substantiated by two field studies where in-situ ozonation was apparently successful at remediating the sites.