The Research On Biosurfactant And Its Application In The Remediation Of Metal-polluted Sediment

Biosurfactant is a high surface-active agent synthesized by microorganism. Compared with chemical surfactant, biosurfactant has a low toxicity to ecological system of Earth and can be biodegraded by microorganism. There are a lot of researches on biosurfactants and their producers, but most researches are focused on microorganisms that are screened for producing biosurfactant. The researches on the biosurfactant-producing ability of microorganisms that have been identified and the reasons for the difference in their ability have not been reported.Four Pseudomonas aeruginosa and two Bacillus subtilis obtained from China Center for Typical Culture Collection (CCTCC) were studied in this research. The results show that there was a great difference in their ability to produce biosurfactant and only two Pseudomonas aeruginosa and one Bacillus subtilis can produce biosurfactant. The optimal nitrogen sources, carbon sources and growth factors were studied by orthogonal experiments. The best conditions for biosurfactant-producing of Pseudomonas aeruginosa and Bacillus subtilis were determined and then two biosurfactants produced by Pseudomonas aeruginosa and Bacillus subtilis were identified by TLC and HPLC-MS. So this research is innovative in the research method.The pollution of sediment by heavy metals is noted by more and more researchers. The researches vary from ecology risk of metal-polluted sediment, the relation between the organic content in the sediment and heavy metal content, to the releasing regulation of heavy metal in the sediment, but the research on the remediation of polluted sediment is a new research field in the world. The research on the metal removal from sediment is still limited to the reports by Mulligan C N.The potential of microbially-produced surfactant (rhamnolipid) to remove cadmium and lead from sediment was investigated in this study. Batch washings were conducted on the sediment with different solution pH and rhamnolipid concentrations. And the speciation of heavy metals in the sediment before and after washing was analyzed by sequential extraction. The results show that rhamnolipid can remove cadmium and lead from sediment efficiently. The heavy metal removal was optimum when the pH of rhamnolipid solution was 10.0, and the removal efficiency was thehighest when the sorption of rhamnolipid on the sediment reached a plateau. The speciation of the heavy metals had an effect on the removal efficiency, and exchangeable and organic fractions could be removed efficiently. Four successive washings removed 80.1% cadmium and 36.5% lead. Biosurfactant rhamnolipid has a low toxicity to ecological system of the Earth and can be recovered by precipitation, so its potential in the remediation of metal-polluted sediment is great.