Effect of rhamnolipids on the dissolution, bioavailability, and biodegradation of phenanthrene

Biodegradation rates for polycyclic aromatic hydrocarbons (PAH) in the environment are limited by their low solubility and sorption to solid surfaces. The purpose of this study was to quantify the effect of biosurfactants on the dissolution, bioavailability, and biodegradation of a slightly soluble PAH, phenanthrene, in a series of batch solution studies. A mathematical model that describes the combined effects of solubilization and biodegradation, including description of bioavailability within surfactant micelles, was used to analyze the experimental results. Two forms of the biosurfactant, a monorhamnolipid and a dirhamnolipid, were tested; it was found that both surfactants increased the solubility and enhanced the rate of phenanthrene biodegradation. Monorhamnolipid was more effective than dirhamnolipid for solubilization; however, overall rates of mineralization were essentially the same. This seems to result from variable bioavailability of substrate:  phenanthrene within monorhamnolipid micelles w...