Asphaltene biodegradation using microorganisms isolated from oil samples

Twenty-five species were isolated from oil and polluted soil samples of Dorood oilfield, in the south of Iran, which were able to utilize asphaltene as a sole carbon and energy sources. Isolated microorganisms, in the form of pure and mixed, were cultured for 2 months at 28 °C in a medium containing asphaltene. Five of the isolated microorganisms which higher growth on asphaltene were identified as Pseudomonas spp TMU2-5, Bacillus licheniformis TMU1-1, Bacillus lentus TMU5-2, Bacillus cereus TMU8-2, and Bacillus firmus TMU6-2. These bacteria degrade 40–46% of asphaltene and among them B. lentus TMU5-2 showed the greatest capability for degradation asphaltene. Biodegradation of asphaltene by the mixed culture of five bacteria was 48%, this is the highest reported degradation result. The bacterial mixed culture growth, in a bubble-column (55 × 7.5 cm), was evaluated by CHN and FTIR analysis during 2 months of incubation. The values of pH, salinity and asphaltene concentration for degradation at 40 °C were optimized by response surface methodology for pure cultures of B. lentus and the optimum results are 6.7, 76 g L−1 and 22 g L−1, respectively, and for the mixed culture as 6.4, 76 g L−1 and 12 g L−1, respectively. Conducted kinetic study showed that the data of asphaltene biodegradation fit to Tessier model and the growth kinetic parameter were obtained as μmax = 0.31 day−1, ks = 39.19 g L−1 and Yxs = 0.21.