During spills of hydrocarbons in soil, it has been observed that aliphatic and the slightly aromatic hydrocarbons are first to be removed, however, branched aliphatic and aromatic compounds, polycyclic aromatic hydrocarbons (PAHs) and their similar heteroatoms with sulfur (PAS) remain strongly absorbed to soil particles. It is important to point out that studies of biodegradation of alkyl-substituted PAHs and PAS are scarce and most of them have been carried out using only available standard compounds. The aim of this investigation was to identify and to quantify the aliphatic, alkyl polycyclic aromatic, and sulfured recalcitrant fractions present in a contaminated soil with drilling wastes. A modified method of shaking-centrifugation extraction was implemented for the extraction of compounds from contaminated soil. The organic extract obtained was purified and fractionated using aluminum oxide. Gas Chromatograph with flame ionization detector (GC-FID) and Gas Chromatograph with mass spectrometer detector (GC-MS) identified the aliphatic, PAHs and PAS fractions. Hydrocarbon composition in the soil contaminated with 140,000 mg TPHs/Kg soil, consisted in 80% of branched aliphatic compounds of C10 to C22, 15% of alkyl PAHs, and 5% of PAS compounds. Lineal, lineal branched, and cyclic branched aliphatic hydrocarbons, as well as their alkyl naphthalene, anthracene and phenantrene, methyldibenzothiophene, dimethyldibenzothiophene, and dimethylnaphto[2,3-b]thiophene compounds were identified by CG-MS. The identification of compounds in soil P31, allowed us to speculate on the origin of the contamination and the natural attenuation that had occurred at this site.

The application of biological processes in restoring oil polluted sites is growing due to their efficiency in removing different classes of pollutants. The aim of this study was to determine the ability of microorganisms present in a drilling-waste polluted soil (36,200 mg TPH kg −1 soil) to remove weathered hydrocarbons under stimulated and non-stimulated soil conditions. The hypothesis under study was whether petroleum hydrocarbons removal could be enhanced by manipulating C/N ratio, water content and addition of three agroindustrial wastes. A Box-Behnken design was employed to evaluate the effect of each variable. Results demonstrated that, for orange peels and banana trunk treatments, the variable with the largest effect (p < 0.01) on hydrocarbon removal was the C/N ratio, indicating that higher ratio (100/3) improved removal (79.5-82%). The largest effect (p < 0.001) on hydrocarbon removal for pineapple wastes was observed with higher water content (60%) achieving the highest removal (89%). After 90 days of experimentation, the type of agricultural waste and the agricultural waste/soil ratio were not statistically significant in any treatment. However, their addition was important relative to non-stimulated soil, which showed a hydrocarbon removal of 17%. Data reported in this study showed the application of bioremediation in clay and drilling waste-polluted soils.