Effect of an emulsifying surfactant on diesel degradation by cultures exhibiting inducible cell surface hydrophobicity

Background: Accumulation of petroleum hydrocarbons in the environment is often attributed to inherently slow degradation rates. This study was conducted to determine if diesel biodegradation by cultures exhibiting inducible cell surface hydrophobicity could be enhanced by addition of a chemical surfactant promoting emulsification. Experiments were designed to determine quantitatively the enhancement in diesel degradation caused by Triton X-100 for two bacterial cultures, Exiguobacterium aurantiacum and Burkholderia cepacia. Results: In the presence of Triton X-100 at twice the critical micelle concentration (CMC) the extent of degradation in whole diesel in 5 days was 1.6-1.8 times that observed over 15 days with no surfactant. The enhancement in overall degradation of diesel range resolved peaks (DRRP, representing n-alkanes and branched alkanes) was 1.76 and 1.26 times for E. aurantiacum and B. cepacia cultures respectively. Although an enhancement in decay rate was observed for all n-alkane components, it was most significant for C19, C25 and pristane. Conclusion: For cultures exhibiting direct interfacial uptake, the beneficial effect of an emulsifying surfactant found here is in contrast to earlier studies reporting a detrimental effect due to detachment of cells from the oil/water interface. Surfactant addition may have significant potential in enhancing degradation of the more recalcitrant components. (C) 2007 Society of Chemical Industry