Enhanced Solubility and Biodegradation of Naphthalene with Biosurfactant

Biosurfactant was produced by fermenting kerosene and used vegetable oil using a Pseudomonas sp. under nonsterile conditions. The biosurfactant at a concentration of 0.5 g/L and pH of 10.5 lowered the surface tension of water to 25 mN/m. The biosurfactant was used to enhance the solubility of naphthalene, and the results are compared to an anionic (sodium dedecyl sulfate) and a nonionic (Triton X-100) surfactant. The biosurfactant (5 g/L at pH of 7) enhanced the solubility of naphthalene to more than 30 times its aqueous solubility. Solubilized naphthalene in Triton X-100 and biosurfactant solutions was biodegraded by the same microorganism that produced the biosurfactant. Naphthalene solubilized in biosurfactant and Triton X-100 (400-600 mg/L) was biodegraded in 40 days and 100 h, respectively. Naphthalene in the amount of 30 mg/L was degraded by the Pseudomonas sp. in 2 days. The biosurfactant was also biodegraded during the biodegradation of naphthalene, but this was not the case with Triton X-100. The biodegradation of the biosurfactant appeared to compete with the biodegradation of naphthalene. Sodium dedecyl sulfate inhibited the biodegradation of naphthalene at the conditions studied.