Sorption and Transport of Naphthalene and Phenanthrene in Silica Sand in the Presence of Rhamnolipid Biosurfactant

Sorption and transport of naphthalene and phenanthrene in silica sand in the presence of rhamnolipid biosurfactant were investigated by batch and column experiments. Naphthalene and phenanthrene had linear sorption isotherms on silica sand with partition coefficients decreasing with increasing rhamnolipid biosurfactant concentrations until the critical micellar concentration (CMC). After the CMC was reached, naphthalene and phenanthrene partition coefficients on silica sand increased with the increase of rhamnolipid biosurfactant concentrations. It was believed that micelles were formed when rhamnolipid biosurfactant was supplied at concentrations higher than the CMC, to which naphthalene and phenanthrene had higher affinity than silica sand. In column experiments, both naphthalene and phenanthrene had early breakthroughs in the presence of rhamnolipid biosurfactant than in its absence. Estimated naphthalene and phenanthrene retardation using naphthalene and phenanthrene batch sorption data was consistent with column experimental observations. Nevertheless, naphthalene and phenanthrene recovery decreased in answer to the presence of rhamnolipid biosurfactant at concentrations greater than the CMC, which was attributed to the entrapment of naphthalene and phenanthrene associated rhamnolipid biosurfactant micelles.