This study investigated biosurfactant production by both free and immobilized bacterial strain of Pseudomonas aeruginosa using waste engine oil as a substrate. Polyurethane foam cubes were used as a carrier for the immobilization. Immobilization of cells using polyurethane foam was found to be convenient and after two days the bacterial growth was 2.9×1014 CFU/ml. The batch experiments were performed in Erlenmeyer flasks and monitored at every 24 hr interval for both free and immobilized cell systems. The microbial population was counted using the plate count method and the hydrocarbon degradation percentage was calculated to evaluate bacterial activity. Surface tension was measured at regular intervals to ensure the presence of biosurfactant. The maximum reduction was found to be 37 and 35 mN/m in free and immobilized cell systems, respectively. The chemical characterization using Fourier transform infrared spectroscopy confirmed the obtained product as rhamnolipid. Biosurfactant yield was found to be maximum in the case of immobilized system which was approximately 18 g/L. Scanning electron micrographs showed the potential of reusing the immobilized cells with polyurethane foam cubes.
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