Optimization of diesel biodegradation by Vibrio alginolyticus using Box-Behnken design

Petroleum hydrocarbons pollutants, such as diesel fuel, have caused ecosystem damage in terrestrial and aquatic habitats. They have been recognized as one of the most hazardous wastes. This study was designed to optimize the effect of Tween 80 concentration, nitrogen (N)/phosphorus (P) ratio and salinity level on diesel biodegradation by Vibrio alginolyticus (V. alginolyticus). Response surface methodology with Box-Behnken design was selected with three factors of Tween 80 concentration (0, 5, 10 mg/L), N/P ratio (5, 10, 15) and salinity level (15 parts per thousand, 17.5 parts per thousand, 20 parts per thousand) as independent variables. The percentage of diesel degradation was a dependent variable for 14 d of the remediation period. The results showed that the percentages of diesel degradation generally increased with an increase in the amount of Tween 80 concentration, N/P ratio and salinity level, respectively. The optimization condition for diesel degradation by V. alginolyticus occurred at 9.33 mg/L of Tween 80, 9.04 of N/P ratio and 19.47 parts per thousand of salinity level, respectively, with percentages of diesel degradation at 98.20%. The statistical analyses of the experimental results and model predictions (R-2 = 0.9936) showed the reliability of the regression model and indicated that the addition of biostimulant can enhance the percentage of diesel biodegradation.