Degradation of crude oil and relationship with bacteria and enzymatic activities in laboratory testing

• Crude oil degradation variables were evaluated by response surface methodology.
• Degradation of crude oil was fitted linearly with biomass and enzyme activities.
• The crude oil biodegradation increased substantially with bacterial biomass.

The biodegradation of petroleum hydrocarbons is one of the most important processes involved in the weathering and eventual removal of petroleum hydrocarbons from the marine environment. The effect of four variables—(NH4)2SO4, K2HPO4, temperature and inoculation—on crude oil biodegradation (BDR) were evaluated using response surface methodology to confirm the nutrients effect on the biodegradation and explore the relationships between BDR and bacterial biomass, dehydrogenase activity and peroxidase activity. These variables were optimized to allow the highest removal of crude oil, and the results indicated that crude oil removal could increase to even higher levels if the temperature and the concentrations of (NH4)2SO4 and K2HPO4 were increased. Following biodegradation, the enzymatic activities were evaluated using a modified spectrophotometric method; the results showed that an increase in the temperature and inoculation quantity resulted in a higher dehydrogenase activity (mg TPF (l·h)−1) and that the highest peroxidase activity (18.50 U) occurred at 2.01 g·l−1 (NH4)2SO4, 1.10 g·l−1 K2HPO4, 25 °C and 1.0% inoculation. The crude oil BDR increased substantially with bacterial biomass and decreased slightly with dehydrogenase activity or peroxidase activity, which was consistent with the coefficients in the fitted equation. The correlation between microbial degradation of crude oil and bacterial biomass and enzymatic activities can be used in simulations of biodegradation processes with petroleum hydrocarbons, PAHs and other hydrocarbon compounds and provides a more thorough understanding of the microbial community's function in contaminated soil.

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