Abstract

Hexavalent chromium is of great concern now as it has highly toxic and carcinogenic properties and also for its potential for the contamination of groundwater due to its greater mobility in soils and in the aquatic environment. The objective of this study is the reduction of hexavalent chromium to trivalent chromium using rhamnolipid both in water and soil media. Rhamnolipid had been used as its toxicity is very low as a commercial surfactant and it is readily biodegradable with a very low environmental impact. Batch experiments were performed to evaluate the feasibility of using rhamnolipid for the removal and reduction of hexavalent chromium from contaminated soil and water. The initial chromium concentration, rhamnolipid concentration, pH and temperature were evaluated and found to affect the reduction efficiency. The rhamnolipid can reduce 100% of initial Cr (VI) in water at optimum conditions (pH 6, 2% rhamnolipid concentration, 25°C) if the concentration is low (10 ppm). For higher initial concentrations (400 ppm), it takes time to reduce (24.4% in one day). In the case of soil, rhamnolipid only can remove the soluble part of the chromium present in the soil. The extraction increased with the increase of initial concentration in soil but decreased slightly with the increase of temperature above 30°C. The reduction trend of the extracted chromium is the same as in water media. A sequential extraction study was used on soil before and after washing to determine from what fraction the rhamnolipid removed the chromium. The exchangeable and carbonate fractions accounted for 24% and 10% of the total chromium, respectively. The oxides and hydroxides portion retained 44% of chromium present in the soil. On the other hand, 10% and 12% of the chromium was associated with the organic and residual fractions. Rhamnolipid can remove most of the exchangeable (96%) and carbonate (90%) portions and some of the oxide and hydroxide portion (22%) but cannot remove chromium from the other fractions. This information is important in designing the appropriate conditions for soil washing