Progressive degradation of crude oil n-alkanes coupled to methane production under mesophilic and thermophilic conditions.

Although methanogenic degradation of hydrocarbons has become a well-known process, little is known about which crude oil tend to be degraded at different temperatures and how the microbial community is responded. In this study, we assessed the methanogenic crude oil degradation capacity of oily sludge microbes enriched from the Shengli oilfield under mesophilic and thermophilic conditions. The microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes combined with cloning and sequencing. Enrichment incubation demonstrated the microbial oxidation of crude oil coupled to methane production at 35 and 55°C, which generated 3.7±0.3 and 2.8±0.3 mmol of methane per gram oil, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that crude oil n-alkanes were obviously degraded, and high molecular weight n-alkanes were preferentially removed over relatively shorter-chain n-alkanes. Phylogenetic analysis revealed the concurrence of acetoclastic Methanosaeta and hydrogenotrophic methanogens but different methanogenic community structures under the two temperature conditions. Candidate divisions of JS1 and WWE 1, Proteobacteria (mainly consisting of Syntrophaceae, Desulfobacteraceae and Syntrophorhabdus) and Firmicutes (mainly consisting of Desulfotomaculum) were supposed to be involved with n-alkane degradation in the mesophilic conditions. By contrast, the different bacterial phylotypes affiliated with Caldisericales, "Shengli Cluster" and Synergistetes dominated the thermophilic consortium, which was most likely to be associated with thermophilic crude oil degradation. This study revealed that the oily sludge in Shengli oilfield harbors diverse uncultured microbes with great potential in methanogenic crude oil degradation over a wide temperature range, which extend our previous understanding of methanogenic degradation of crude oil alkanes.

Qualitative and quantitative analysis of dibenzothiophene, its methylated homologues, and benzonaphthothiophenes in crude oils, coal, and sediment extracts.

Polycyclic aromatic sulfur heterocyclics (PASHs) consist mainly of thiophene class compounds, and are the most important organosulfur compounds in crude oils and sediment extracts. Dibenzothiophene (DBT) and its methylated homologues were identified on mass chromatograms by comparison with retention indices published in the literature. Some isomers of dimethyldibenzothiophene and trimethyldibenzothiophene that were tentatively identified in previous reports have been determined here by comparison with calculated retention indices and taking the substitution pattern of the methyl groups into account. The response factors relating that of dibenzothiophene to internal standards were obtained by GC-MS analyses of mixture solutions with different concentration ratios. We concluded that DBT-d8 (octadeutero-dibenzothiophene) is the optimal internal standard for quantitative analyses of the thiophene compound class in oils, coal, and sediment extracts. Calibration experiments for each class of compounds are absolutely necessary when quantifying polycyclic aromatic hydrocarbons and other heterocyclics with a stable isotope labeled internal standard.