SOLUBILIZATION OF NAPHTHALENE AND METHYL-SUBSTITUTED NAPHTHALENES FROM CRUDE-OIL USING BIOSURFACTANTS

Glycolipids produced by Rhodococcus species H13-A and a representative synthetic surfactant Tween-80 (polyoxyethylene sorbitan monooleate) w ere used to demonstrate enhanced substrate ''solubility'' (aqueous-plu s-micellar phase) in the presence of surfactants. Nascent concentratio ns of naphthalene and its methyl-substituted derivatives in crude oil were used as representative polycyclic aromatic hydrocarbons for the s tudy. Both bio-surfactant glycolipids from H13-A and Tween-80 lowered the surface tension of aqueous solutions from 72 to similar to 30 dyn/ cm. The two-ring aromatics showed a substantial increase in their appa rent solubilities in the presence of surfactants; the increase being s ignificantly greater far the biosurfactant as compared to the syntheti c surfactant. The aqueous phase solubility enhancement was greater for the highly substituted derivatives as compared to the lesser substitu ted compounds. Higher toxicity levers, as seen by the lower EC(50) val ues, of the surfactant mixtures indicated enhanced partitioning of the petroleum contaminants in the aqueous phase. Higher initial EC(50) va lues for the biosurfactant meant that they exhibit lesser aqueous toxi city as compared to the synthetic surfactant When compared on a toxici ty per mass of PAH basis, the end point Tween-80 system was approximat ely 50% more toxic than the biosurfactant system.