PRODUCTION AND USE OF BIOSURFACTANTS IN BIOREMEDIATION OF HEAVY METAL POLLUTED SOIL

Abstract

ABSTRACT Bacteria were isolated from waste lubricating oil polluted soil and screened for potential to produce biosurfactants using oil spreading or displacement, oil drop collapse, emulsification, and blood haemolysis methods. Of the 45 isolates, 20 isolates (44.44 %) were positive for oil spreading, 22 isolates (48.89%) had haemolytic activity (β and α), 5 isolates (11.11%) were able to collapse oil droplet within 30seconds and 7(15.56%) were good emulsifiers. Based on these capabilities and consistency in activity, five of the isolates emerged for biosurfactant production. They were identified as Pseudomonas aeruginosa MPE40, Micrococcus kristinea MPE12, Acinetobacter iwoffi MPE25, Bacillus firmus MPE30, and Pseudomonas paucimobilis MPE17. Strains MPE40, MPE30, MPE25, MPE17 and MPE12 generated 1.7g/100ml, 1.6g/100ml, 1.6g/100ml, 1.0g/100ml, and 0.8g/100ml of biosurfactant after 7days respectively in the presence of 1% (v/v) diesel as sole source of carbon and energy. Biochemical, physical, chemical characterization as well as identification of the functional groups of the biosurfactants were done using TLC, GC-MS and FTIR. Chemical analyses of the biosurfactants indicated that they were glycolipids, composed majorly of Palmitic Hexadecanoic, Octadecanoic acid, methyl esters and hydroxylated fatty acids linked to a decanoic acid. Fourier transform infrared analysis showed that the surfactants consisted of carboxyl, hydroxyl, amino and sugar derivative groups. Specifically, strains MPE40, MPE30, MPE25, MPE17 and MPE12 produced the biosurfactants designated Rhamnolipid Bios-40, Firmnolipid Bios-30, Sulfoglycolipid Bios-25, Glycolipopeptide Bios-17, Disulfoglycolipid Bios-12 respectively. The potential of the biosurfactants for heavy metal removal in soil was also studied and the results revealed percentage removal in the range of 68.05%−95.5% for lead (Pb) and 75.7%−91.0% for chromium (Cr). It was further observed that pH of the heavy metal contaminated soil amended with biosurfactants was low (5.24-6.71 for Pb and 4.57-6.21 Cr. contaminated soil) as compared to that of original unpolluted soil (6.78) this indicates high removal of metals from the contaminated soil and effective remediation of metals with the biosurfactants. The metal adsorption by rhamnolipids Bios-40 of Pseudomonas aeruginosa was found to be more effective both to lead and chromium, although others had a comparative satisfactory removal. Thus, the results suggest that the biosurfactant have the potential to be used as an alternative remediation tool for treatment of soil contaminated with heavy metals.