Application of Rhamnolipid and Surfactin for Enhanced Biodegradation of Diesel-Contaminated Water and Soil

摘要

Bioremediation of petroleum hydrocarbons has been proposed as an effective, economic, and environmentally friendly technology, although bioavailability of hydrophobic organic compounds (HOCs) to microorganisms could be a limiting factor during the biodegradation process. This study investigated the potential application of two biosurfactants, surfactin (SF) and rhamnolipid (RL), for enhanced biodegradation of diesel-contaminated water and soil with series of bench-scale experiments. In diesel/water batch experiments, addition of 40 mg/L of SF significantly enhanced biomass growth as well as diesel biodegradation percentage, compared to no SF addition. Addition of SF more than 40 mg/L, however, decreased both biomass growth and diesel biodegradation efficiency, with a worst diesel biodegradation percentage at 400 mg/L of SF addition. Similar trends were also observed for specific biomass growth rate and specific diesel degradation rate constant as SF addition increased from 0 to 400 mg/L. Addition of RL to diesel/water systems from 0 to 80 mg/L substantially increased biomass growth and diesel biodegradation percentage from 1000 to 2500 mg VSS/L and 40 to 100%, respectively. RL addition at a concentration of 160 mg/L provided similar results to those of 80 mg/L addition. In diesel-water systems with 50 mg/L of RL addition, an optimum pH condition for microbial growth and diesel biodegradation was found to be at a pH 7.2, while decreasing pH to 5.2 or increasing it to 8.4 reduced those parameters considerably. For the cases where 40 mg/L of SF was added, the enhancing ability shared a general trend with that observed for adding 50 mg/L of RL as the pH increased from 5.2 to 7.2. Finally, potential application of SF and RL in stimulating indigenous microorganisms for enhanced bioremediation of diesel-contaminated soil was also examined. The results confirmed their enhanced capability in both efficiency and rate of diesel biodegradation in diesel/soil systems.