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Monorhamnolipid and it’s mixture with di-rhamnolipid biosurfactant reported so far for removal of heavy metals form contaminated soil has high Critical Micelle Concentration (CMC) value of 40-50mg/L indicating low surface active properties and heavy metal removal ability. Complexation of cadmium by a di-rhamnolipid biosurfactant produced by Pseudomonas aeruginosa strain BS2 was studied in batch solutions and soil experiments. Conditional stability constants (log KL) for metal rhamnolipid (0.15%) complexation in a buffered medium (0.1 M Pipes, pH 6.8) were determined using an ion exchange technique and averaged to 0.1543 for cadmium and 0.6781 for lead. The efficiency of biosurfactant-facilitated removal of soil bound metal is affected by biosurfactant sorption to soil. In this study, batch experiments were performed to minimize rhamnolipid sorption and to optimize rhamnolipid application for removal of cadmium from spiked soil. The contaminated as well as uncontaminated soils were treated first with KNO3 electrolyte solution (0.1M, pH 6.8) and then with rhamnolipid solution (0-7.5 mg). Results showed that in-uncontaminated soil, 29.62 % of rhamnolipid was sorbed against 7.84 % in cadmium-spiked soil. Batch experiment set up to optimize weight: volume ratio of soil: rhamnolipid showed that 36.4 % cadmium was removed from a soil: rhamnolipid ration of 1:10 which appears to be maximum. A similar kind of batch experiment was set up to observe the effect of rhamnolipid treatment time on metal removal. Results have demonstrated that maximum 92 % cadmium desorption occurs at 36 hrs of rhamnolipid treatment. Rhamnolipid treatment was found to be very effective in removal of cadmium form spiked soil containing cadmium concentrations up to 1000 mg/kg.
