Biodegradation of aged polycyclic aromatic hydrocarbons (PAHs) by microbial consortia in soil and slurry phases

Microbial consortia isolated from aged oil-contaminated soil were used to degrade 16 polycyclic aromatic hydrocarbons (15.72 mgkg(-1)) in soil and slurry phases. The three microbial consortia (bacteria, fungi and bacteria-fungi complex) could degrade polycyclic aromatic hydrocarbons (PAHs), and the highest PAH removals were found in soil and slurry inoculated with fungi (50.1% and 55.4%, respectively). PAHs biodegradation in slurry was lower than in soil for bacteria and bacteria-fungi complex inoculation treatments. Degradation of three- to five-ring PAHs treated by consortia was observed in soil and slurry, and the highest degradation of individual PAHs (anthracene, fluoranthene, and benz(a)anthracene) appeared in soil (45.9-75.5%, 62-83.7% and 64.5-84.5%, respectively) and slurry (46.0-75.8%, 50.2-86.1% and 54.3-85.7%, respectively). Therefore, inoculation of microbial consortia (bacteria, fungi and bacteria-fungi complex) isolated from in situ contaminated soil to degrade PAHs could be considered as a successful method.     

Bio-treatment of oily sludge: the contribution of amendment material to the content of target contaminants, and the biodegradation dynamics

The objective was to investigate the aerobic biodegradation of oily sludge generated by a flotation-flocculation unit (FFU) of an oil refinery wastewater treatment plant. Four 1m(3) pilot bioreactors with controlled air-flow were filled with FFU sludge mixed with one of the following amendments: sand (M1); matured oil compost (M2); kitchen waste compost (M3) and shredded waste wood (M4). The variables monitored were: pH, total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs), total carbon (C(tot)), total nitrogen (N(tot)) and total phosphorus (P(tot)). The reduction of TPH based on mass balance in M1, M2, M3 and M4 after 373 days of treatment was 62, 51, 74 and 49%; the reduction of PAHs was 97%, +13% (increase), 92 and 88%, respectively. The following mechanisms alone or in combination might explain the results: (i) most organics added with amendments biodegrade faster than most petroleum hydrocarbons, resulting in a relative increase in concentration of these recalcitrant contaminants; (ii) some amendments result in increased amounts of TPH and PAHs to be degraded in the mixture; (iii) sorption-desorption mechanisms involving hydrophobic compounds in the organic matrix reduce bioavailability, biodegradability and eventually extractability; (iv) mixture heterogeneity affecting sampling. Total contaminant mass reduction seems to be a better parameter than concentration to assess degradation efficiency in mixtures with high content of biodegradable amendments.     

Electrokinetic remediation of metals and organics from historically contaminated soil

The electrokinetic remediation of an historically contaminated soil is described. The soil was contaminated with a range of metals including lead, zinc, manganese, copper and arsenic, polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene (BTEX). A small‐scale experiment (973.2 g dry weight soil), utilising a planar electrode configuration, investigated the potential for moving metals and organics. After 23 days treatment at a current density of 3.72 A /m⁻², 44% of calcium and 29% of manganese were removed from the soil at the cathode. Of the other contaminating metals, zinc and lead moved towards the cathode, but with no significant removal from the soil. Movement of PAHs was also observed, with a 94% reduction in concentration in the third of the soil closest to the anode after 23 days. A larger scale experiment (46.7 kg dry weight soil) utilised a hexagonal array of tubular anodes surrounding a central tubular cathode. Treatment for 112 days led to acidification of the soil to pH 2.59 closest to the anode in a direct line between the anode and cathode. Soil not directly in line between the electrodes was not acidified significantly. Movement of metal ions was observed, in line with the electrodes, with concentrations of lead and arsenic increasing to 162% and 171% of starting concentrations closest to the anode, respectively, and those of zinc, copper and manganese decreasing to 42%, 68% and 57%, respectively. At positions not directly in line with the electrodes, no significant metal movements were observed. Overall, there was no significant removal of contaminating metals from the soil. PAHs and BTEX compounds were moved by electroosmosis towards the cathode, with soil concentrations of PAHs reduced from 720 mgkg⁻¹ to 4.7 mgkg⁻¹ after 22 days. PAHS (28 mg) and benzene (9660 mg) were recovered in granular activated carbon (GAC) columns. © 2000 Society of Chemical Industry     

Polycyclic aromatic hydrocarbons (PAHs) in sugarcane juice

Sugarcane juice is a common beverage in many Brazilian cities. At harvesting season most sugarcane plantation is burnt and this procedure has been shown as an important source of PAHs emission. In the present study 80 samples of sugarcane juice collected from two Brazilian cities, in two different periods, were analysed for the presence of four PAHs: benz(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene and benzo(a)pyrene. PAHs were detected in 50% of the samples. The samples collected between harvests presented mean sums of PAHs of 0.013 μg/kg and 0.012 μg/kg, while the samples collected during harvest presented mean sums of 0.053 μg/kg and 0.055 μg/kg. A higher concentration and incidence of PAHs in the juices collected in the harvest period was verified, corroborating the burning of the crops as a source of sugarcane juice contamination.     

An experimental and numerical study of the effects of dimethyl ether addition to fuel on polycyclic aromatic hydrocarbon and soot formation in laminar coflow ethylene/air diffusion flames

The effects of dimethyl ether addition to fuel on the formation of polycyclic aromatic hydrocarbons and soot were investigated experimentally and numerically in a laminar coflow ethylene diffusion flame at atmospheric pressure. The relative concentrations of polycyclic aromatic hydrocarbon species and the relative soot volume fractions were measured using planar laser-induced fluorescence and two-dimensional laser-induced incandescence techniques, respectively. Experiments were conducted over the entire range of dimethyl ether addition from pure ethylene to pure dimethyl ether in the fuel stream. The total carbon mass flow rate was maintained constant when the fraction of DME in the fuel stream was varied. Numerical calculations of nine diffusion flames of different dimethyl ether fractions in the fuel stream were performed using a detailed reaction mechanism consisting of 151 species and 785 reactions and a sectional soot model including soot radiation, inception of nascent soot particle due to collision of two pyrene molecules, heterogeneous surface growth and oxidation following the hydrogen abstraction acetylene addition mechanism, soot particle coagulation, and PAH surface condensation. The addition of a relatively small amount of dimethyl ether to ethylene was found experimentally to increase the concentrations of both polycyclic aromatic hydrocarbons and soot. The synergistic effect on polycyclic aromatic hydrocarbons persists over a wider range of dimethyl ether addition. The numerical results reproduce the synergistic effects of dimethyl ether addition to ethylene on both polycyclic aromatic hydrocarbons and soot, though the magnitude of soot volume fraction overshoot and the range of dimethyl ether addition associated with the synergistic effect of soot are less than those observed in the experiment. The synergistic effects of dimethyl ether addition to ethylene on many hydrocarbon species, including polycyclic aromatic ones, and soot can be fundamentally traced to the enhanced methyl concentration with the addition of dimethyl ether to ethylene. Contrary to previous findings, the pathways responsible for the synergistic effects of benzene, polycyclic aromatic hydrocarbons, and soot in the ethylene/dimethyl ether system are found to be primarily due to the cyclization of l-C₆H₆ and n-C₆H₇ and to a much lesser degree due to the interaction between C2 and C4 species for benzene formation, rather than the propargyl self-combination reaction route, though it is indeed the most important reaction for the formation of benzene.     

新疆典型地区土壤/松针中多环芳烃分布特征

考察了新疆典型地区(石河子、北屯和喀纳斯)土壤和松针中多环芳烃(PAHs)的浓度水平和分布特征。与国内外典型地区相比,新疆土壤和松针中PAHs的污染水平较低。与受人类活动影响明显的石河子地区相比,人迹罕至的喀纳斯地区土壤和松针中低分子量PAHs的比例较高,而高分子量PAHs的比例较低,不同环数PAHs呈现出明显的“局部分馏”现象。PAHs在土壤/松针中的分布系数与其过冷液体饱和蒸气压具有显著的对数线性关系,表明PAHs在土壤/松针中的分布受其物理化学参数的影响,PAHs在土壤/相似文献   

The role of support on the performance of platinum-based catalysts for the total oxidation of polycyclic aromatic hydrocarbons

A range of Pt supported catalysts have been evaluated for the total oxidation of naphthalene. Catalysts contained 0.5 wt% Pt on a range of supports (γ-Al₂O₃, TiO₂, SiO₂, SnO₂, and CeO₂₎. SiO₂ was the best support, the 0.5%Pt/SiO₂ catalyst showing a conversion to carbon dioxide of over 90% at 200 °C (100 vppm naphthalene, GHSV = 45,000 h⁻¹). The catalyst also showed a considerably higher activity (in the temperature range 100–175 °C) than a CeO₂ catalyst recently reported to be one of the most effective catalysts for the total oxidation of naphthalene. The high activity of the 0.5%Pt/SiO₂ catalyst has been attributed to the relatively low dispersion and relatively large size of Pt particles. Furthermore, due to the acidic and non-reducible nature of the SiO₂, platinum is expected to have a weak interaction with the support. XPS data identified the presence of Pt⁰ on the surface and this contributes to the high activity.     

Composite Fe3O4/Humic Acid Magnetic Sorbent and its Sorption Ability for Chlorophenols and some other Aromatic Compounds

A composite magnetic sorbent with a relatively high content of humic substances (above 35% of organic carbon) was prepared by co-precipitation of Fe²⁺/Fe³⁺ salts with commercially available alkaline humate concentrate. Magnetite (Fe₃O₄) was identified as the main crystalline phase bearing the magnetic properties of the sorbent. Scanning electron microscope (SEM) images revealed the presence of uniform sub-micron structures on the surface of the sorbent grains. Due to the presence of humic substances, the sorbent exhibited good sorption ability towards low-polarity organic pollutants, namely chlorophenols. The sorption efficiency increased in the order of 4-mono- < 2,4-di- < 2,4,5-trichlorophenol in accordance with growing hydrophobicity of these compounds, confirming a hydrophobic nature of the interactions involved in the sorption process. Similar trends were found in the desorption study utilizing water and methanol as leachants. Some polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, fluoranthene, pyrene) were also retained on the sorbent. The chemical composition as well as the main physical characteristics (surface area, phase composition) of the sorbent remained virtually unchanged during the sorption process. The sorbent retained its magnetic properties during the sorption of organic substances from aqueous solutions, which provides an opportunity for its regeneration.     

Case study of the relationship between fungi and bacteria associated with high-molecular-weight polycyclic aromatic hydrocarbon degradation

Although bacteria play dominant roles in microbial bioremediation, few of them have been reported that were capable of utilizing high-molecular-weight (HMW) organic pollutants as their sole sources of carbon and energy. However, many soil fungi can metabolize those of pollutants, although they rarely complete mineralization. In this paper, we investigated the dynamic relationship between fungi and bacteria associated with degradation of HMW-polycyclic aromatic hydrocarbons (PAHs). Artificial fungal-bacterial mixed cultures were constructed to simulate the environment of actual polluted sites. Four bacterial strains and seven fungal strains were isolated that related to the removal of phenanthrene, fluoranthene and pyrene in the soil. Furthermore, these strains were used to create mixed culture of bacteria (Bact-mix), mixed culture of fungi (Fung-mix), fungal-bacterial co-cultures (Fung-Bact), respectively. The maximal pyrene removal rate (67%, 28days) was observed in the Fung-Bact, compared with cultures of Fung-mix (39%) and Bact-mix (56%). The same tendency was also indicated in the degradation of phenanthrene and fluoranthene. In addition, a dynamic relationship during the degradation process between fungi and bacteria was monitored through using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method.