Optimum conditions for washing of crude oil-contaminated soil with biosurfactant solutions

This paper presents the optimum conditions for washing Ekofisk crude oil-contaminated soil with biosurfactant solutions using the Taguchi experimental design method. The optimum values obtained through experimental runs were used to predict crude oil removed at three confident intervals (90, 95 and 99%). Results obtained through experimental runs and predicted crude oil removal were compared and used to access the robustness of the washing method. The biosurfactants tested were aescin, lecithin, rhamnolipid, saponin, tannin and a synthetic surfactant, sodium dodecyl sulphate. The experimental parameters and their four value levels investigated were: temperature (5, 20, 35 and 50°C); concentration of surfactant solutions (0.004, 0.02, 0.1 and 0.5%-mass); volume of surfactant solutions (5, 10, 15 and 20 ml); shaking speed (80, 120, 160 and 200 strokes/min) and washing time (5, 10, 15 and 20 min). Results showed that the optimum washing conditions for temperature and time were found to be 50°C and 10 min for all the surfactant solutions. The other parameters show optimum values at different point. However, SDS, rhamnolipid and saponin show an oil removal of greater than 79%. The washing method was found to be more stable at error of ±1% for all the surfactant solutions except aescin and lecithin. Therefore, we suggest the applicability of this method in decontaminating crude oil-contaminated soil at the field scale.