In this research, the potential of cadmium removal from aqueous solution by foam flotation with a rhamnolipid biosurfactant sample was studied. The effects of different major operating conditions, such as rhamnolipid and cadmium concentrations, solution pH, aeration rate, and frother type and concentration, on the cadmium removal were investigated. The selectivity coefficients in the presence of rhamnolipid maintained definite orders as follows: cadmium > zinc, cadmium > copper, and zinc > copper. The selectivity coefficient of cadmium over copper was the highest one. The maximum removals of Cd from clean and Zn-and Cu-contaminated solutions were about 57%, 36%, and 48%, respectively. Kinetic studies indicated that ion flotation of cadmium follows a first-order equation with a kinetic rate of 0.0071 min −1 . Although the removals are rather low, it seems that the use of rhamnolipid biosurfactant can be promising in heavy-metal removal from wastewaters by foam flotation with some modifications.

A potent biosurfactant-producing bacterial strain isolated from spoiled apples was identified by 16S rRNA as Pseudomonas aeruginosa MA01. Compositional analysis revealed that the extracted biosurfactant was composed of high percentages of lipid (66%, w/w) and carbohydrate (32%, w/w). The surface tension of pure water decreased gradually with increasing biosurfactant concentration to 32.5 mN m(-1) with critical micelle concentration (CMC) value of 10.1 mg L(-1). The Fourier transform infrared spectrum of extracted biosurfactant confirmed the glycolipid nature of this natural product. Response surface methodology (RSM) was employed to optimize the biosynthesis medium for the production of MA01 biosurfactant. Nineteen carbon sources and 11 nitrogen sources were examined, with soybean oil and sodium nitrate being the most effective carbon and nitrogen sources on biosurfactant production, respectively. Among the organic nitrogen sources examined, yeast extract was necessary as a complementary nitrogen source for high production yield. Biosurfactant production at the optimum value of fermentation processing factor (15.68 g/L) was 29.5% higher than the biosurfactant concentration obtained before the RSM optimization (12.1 g/L). A central composite design algorithm was used to optimize the levels of key medium components, and it was concluded that two stages of optimization using RSM could increase biosurfactant production by 1.46 times, as compared to the values obtained before optimization.