Influence of Dispersant/Oil Ratio on the Bacterial Community Structure and Petroleum Hydrocarbon Biodegradation in Seawater

Dispersant is widely used in spill oil response treatment, and the addition of dispersant may influence the biodegradation of total petroleum hydrocarbon (TPH). Dispersant GM-2 was applied to the petroleum polluted seawater in a simulated experiment of an oil spill accident. PCR-RFLP (Restricted Fragment Length Polymorphisms) technique was used to explore the bacterial community structure when dispersant /oil ratio (DOR) is 10%, 20% and 30%, respectively. Results showed the predominant bacterial genera in seawater after the addition of dispersant includes: Alcanivorax, Marinomonas, Flavobacterium, Achromobacter, Parvibaculum, Thalassospira xianhensis and Ochrobactrum. Compared with the most similar bacteria strains after sequencing and analyzing, it is found that the proportion of bacteria unable to hydrolyze Tween80 decrease as well as the alkane degrading bacteria. However, the percentage of the PAHs (Polycyclic aromatic hydrocarbons) and LAS (linear alkylbenzene sulfonate) degrading bacteria increases. Results from the biodegradation study showed that the degradation half-time of TPH decrease from 26.7 d to 19.8 d, 16.1 d and 15.1 d when DOR increased from 0 to 10%, 20% and 30%, so the degradation halftime reduced by 25.7%, 39.5% and 43.5%, respectively. The experiment indicated that in the process of adding GM-2 to oil polluted seawater until DOR reached 30%, the percentage of bacteria that adapt to the surfactant or specialized in the degradation of PAHs and LAS increase, and this spontaneous adjustment accelerates the biodegradation rate of TPH.