Effects of surfactant and oxidant on bioremediation of contaminated soil by total petroleum hydrocarbons using indigenous bacteria

In the present study, solid-phase reactors on microcosm scale were performed to determine optimal conditions to remediate an aged petroleum hydrocarbons contaminated soil (9.1%) by biostimulation. Soil microcosms were incubated for 90 days, maintaining soil moisture at 30%. In the first step, effects of surfactant (Tween 80) and oxidant (H2O2) on the removal efficiency of total petroleum hydrocarbons (TPHs) were investigated without nutrients amendment of contaminated soil. After 90 days of treatment, results showed that Tween 80 did not improve significantly TPHs removal efficiency with only 38 +/- 0.53% at tested concentration of 0.6 g/kg of dry soil, while 47.2 +/- 3.6% were achieved by addition of 1.30 mol H2O2/kg of dry soil. Moreover, an increase in microbial population was recorded regardless of the concentrations of Tween 80 or H2O2 used despite the nutrient deficit with C/N/P molar ratio of 3017/5/1. In the second step, soil amendment by adjusting C/N/P molar ratio to 100/10/1 was tested alone and in the presence of optimal concentrations of Tween 80 and/or H2O2. Results show a significant enhancement in TPHs removal efficiency between 59.6 and 71.9%. The highest TPHs degradation was achieved in the case of nutrients, Tween 80 and H2O2 addition (100/10/1, 0.6 g Tween 80/kg of dry soil and 1.3 mol H2O2/kg of dry soil). The determination of aliphatic and polycyclic aromatic hydrocarbons levels showed a significant drop in aliphatic and aromatic fractions of 71 and 83%, respectively. Furthermore, the use of Tween 80 and H2O2 accelerated the biodegradation process.