Impact of bioaugmentation of soil with n-hexadecane-degrading bacteria and phosphorus source on the rate of biodegradation in a soil-slurry system

In recent years, n-hexadecane, a component of diesel petroleum hydrocarbons, is frequently detected as the contaminant in many soils and water resources. The main aims of this study were focused on the feasibility of using the biodegradation for the removal of n-hexadecane from the soil-slurry system, by assessing the effects of phosphorus sources on biodegradation rate and determining the optimal conditions of the process. This study was carried out using an experimental method at the laboratory scale. The Taguchi method was used to optimize variables and their levels using the Qualitek-4 (w32b) software. We investigated the effects of initial concentration of n-hexadecane as the sole source of carbon (1-80 g/kg of soil), the role of phosphorus sources, at the concentration ranges from 10 to 600 g per kg of soil, released by different bacterial species (Acinetobacter radioresistens, Pseudomonas aeruginosa, Bacillus subtilis, and the bacterial consortium) at the incubation time between 0 and 30 days. The optimum values of the response variables were predicted through signal-to-noise ratio (S/N). Results indicated that Bacillus subtilis were more effective in n-hexadecane degradation compared to the others (42%). Optimization process by Taguchi method suggested that the optimal conditions for the removal of n-hexadecane in a soil-slurry system are as follows: the initial n-hexadecane concentration as sole source of carbon in soil, Na2HPO4.12H2O as phosphorus source at the concentration of 300 mg per kg of soil and, finally, level of significance for the study parameters were 74.31, 6.48 and 8.51, respectively. In conclusion, bioaugmentation of soil with n-hexadecane-degrading bacteria providing an adequate supply of phosphorus source may enhance the biodegradation rate in a polluted soil.