Optimization and characterization of biosurfactant production from kitchen waste oil using Pseudomonas aeruginosa

Kitchen waste oil (KWO) from catering industries or households was used as a low-cost carbon source for producing biosurfactants by self-isolated Pseudomonas aeruginosa. Fermentation performance with KWO was superior to those with four other carbon sources, with higher optical density (OD₆₀₀) of 2.33 and lower interfacial tension of 0.57 mN/m. Culture conditions for biosurfactant production were optimized, with optimal pH of 8.0 and nitrogen source concentration of 2.0 g/L, respectively. The results of infrared spectroscopy and liquid chromatography-mass spectrometry (LC-MS) showed that the biosurfactant was a mixture of six rhamnolipid congeners, among which Rha-Rha-C₁₀-C₁₀ and Rha-C₁₀-C₁₀ were the main components, with mass fraction of approximately 34.20 and 50.86%, respectively. The critical micelle concentration (CMC) obtained was 55.87 mg/L. In addition, the rhamnolipids exhibited excellent tolerance to temperature (20-100 °C), pH (6.0-12.0), and salinity (2-20%; w/v) in a wide range, thereby showing good stability to extreme environmental conditions. The rhamnolipids positively affected oil removal from oil sludge and KWO-contaminated cotton cloth, with removal rate of 34.13 and of 30.92%, respectively. Our results demonstrated that biosurfactant production from KWO was promising, with advantages of good performance, low cost and environmental safety.