Statistical optimization of biosurfactant production using waste biomaterial and biosorption of Pb²⁺ under...

The present study was conducted to statistically optimize the biosurfactant production yield of Pseudomonas sp. F5 using raw orange peel extract (Central composite design (CCD) design; Surface tension (ST) reduction = 32.41 dyne/cm; biosurfactant yield = ~2.4 g/L). The extracted biosurfactant was characterized as a glycolipid having predominant mono-rhamnolipids than di-rhamnolipids with a critical micelle concentration (CMC) of 40 mg/L. The potential of strain F5 for good biosurfactant yield during Pb²⁺ stress and the inherent mechanism for simultaneous biosorption of Pb²⁺ was also investigated. During concomitant submerged fermentation from 100 to 500 mg/L of Pb²⁺ showed enhancement in adsorption capacity from 99.44 to 267.86 mg/g respectively having 60.33 ± 2.87 of emulsification index (E₂₄%) measured at 100 mg/L Pb²⁺ corresponding to maximum biosurfactant production during metal stress. The bacterium showed a high Pb²⁺ MIC (minimum inhibitory concentration) of 2200 mg/L and efficiently biosorbed Pb²⁺ ions at pH 7 and a dosage of 0.05 g under varying initial metal ion concentration and contact time. The exothermic biosorption (chemisorption) mechanism was found to be fitted well with Langmuir (R² = 0.9859) and Pseudo second-order kinetic model (R² = 0.9975; 200 mg/L) having a maximum adsorption capacity of 294.12 mg/g. These findings indicated the excellent potential of biosurfactant producing strain F5 in the removal of Pb²⁺ ions from aqueous system and management of agrowastes as suitable carbon substrate.