Enhancing solubilization of sparingly soluble organic compounds by biosurfactants produced by Nocardia erythropolis

The goal of this research was to produce nontoxic, biodegradable surfactants from Nocardia erythropolis (American Type Culture Collection [ATCC] 4277) and to investigate their potential for enhancing the solubility of sparingly soluble organic compounds (SSOCs). After biosurfactants were harvested from the culture broth, SSOC removal capabilities from aqueous systems by micelles and monomers were determined. Nocardia erythropolis was grown in a 500-mL batch reactor with n-hexadecane as the sole carbon source. Surface tension of the mineral salts medium dropped from 64 dyne/cm to 41 dyne/cm within 24 hours after inoculation with an acclimated culture of N. erythropolis, indicating the production of appreciable quantities of surface-active agents. The lowest surface tension value of 35.2 dyne/cm was reached in 4 days. Maximum production of surfactant was also observed at 4 days. Sparingly soluble organic compounds were partitioned into surfactant micelles that form when the surfactant concentration exceeds the critical micelle concentration. Sparingly soluble organic compound partitioning into micelles increased with decreasing SSOC solubility. The partition constants by micelles were 0.002 0, 0.008 6, and 0.041 2 L/mg for toluene, p-xylene, and trimethylbenzene, respectively. The partitioning capacity of p-xylene by the biosurfactants produced from N. erythropolis was an order of magnitude greater than that by the synthetic surfactant sodium dodecylsulfate (SDS).