Surface tension technique as a strategy to evaluate the adsorption of biosurfactants used in soil remediation

This study investigated the adsorption of two biosurfactants, non ionic saponin and anionic Reco 10 (a mixture of rhamnolipids). The experiments were performed with three different soils (sandy clay loam, clay loam, clay) and at two soil/biosurfactant ratios, m/V=1/10 and 1/40. Using a tensiometer, surface tension in aqueous biosurfactant solutions and their supernatants was measured and the critical micelle concentration (CMC) was determined. The amount of adsorbed biosurfactants was calculated based on the CMC values. Adsorption of both biosurfactants depended on soil type and m/V ratio. The highest saponin and Reco 10 adsorption was in the soil with the greatest content of clay and organic matter, the highest cation exchange capacity and a m/V of 1/40. Thus, clay soils may need a higher concentration of biosurfactants than sandy or loamy soils for effective pollutant removal.