title: Application of biosurfactants, rhamnolipid, and surfactin, for enhanced biodegradation of diesel-contaminated water and soil.
abstract: This study investigated potential application of two biosurfactants, surfactin (SF) and rhamnolipid (RL), for enhanced biodegradation of diesel-contaminated water and soil with a series of bench-scale experiments. The rhamnolipid used in this study, a commonly isolated glycolipid biosurfactant, was produced by Pseudomonas aeruginosa J4, while the surfactin, a lipoprotein type biosurfactant, was produced by Bacillus subtilis ATCC 21332. Both biosurfactants were able to reduce surface tension to less than 30 dynes/cm from 72 dynes/cm with critical micelle concentration (CMC) values of 45 and 50 mg/L for surfactin and rhamnolipid, respectively. In addition, the results of diesel dissolution experiments also demonstrated their ability in increasing diesel solubility with increased biosurfactant addition. In diesel/water batch experiments, an addition of 40 mg/L of surfactin significantly enhanced biomass growth (2500 mg VSS/L) as well as increased diesel biodegradation percentage (94%), compared to batch experiments with no surfactin addition (1000 mg VSS/L and 40% biodegradation percentage). Addition of surfactin more than 40 mg/L, however, decreased both biomass growth and diesel biodegradation efficiency, with a worse diesel biodegradation percentage (0%) at 400 mg/L of SF addition. Similar trends were also observed for both specific rate constants of biomass growth and diesel degradation, as surfactin addition increased from 0 to 400 mg/L. Addition of rhamnolipid to diesel/water systems from 0 to 80 mg/L substantially increased biomass growth and diesel biodegradation percentage from 1000 to 2500 mg VSS/L and 40 to 100%, respectively. Rhamnolipid addition at a concentration of 160 mg/L provided similar results to those of an 80 mg/L addition. Finally, potential application of surfactin and rhamnolipid in stimulating indigenous microorganisms for enhanced bioremediation of diesel-contaminated soil was also examined. The results confirmed their enhancing capability on both efficiency and rate of diesel biodegradation in diesel/soil systems.
authors.affiliation: Department of Environmental Engineering, National Cheng Kung University, No. 1, University Road, Tainan 701, Taiwan, ROC. whang@mail.ncku.edu.tw
authors.forename: Liang-Ming
authors.initials: LM
authors.lastname: Whang
authors.forename: Pao-Wen G
authors.initials: PW
authors.lastname: Liu
authors.forename: Chih-Chung
authors.initials: CC
authors.lastname: Ma
authors.forename: Sheng-Shung
authors.initials: SS
authors.lastname: Cheng
mesh_terms: D001673:Biodegradation, Environmental / Q000187:drug effects; D005742:Gasoline / Q000382:microbiology*; D006017:Glycolipids / Q000494:pharmacology*; D055666:Lipopeptides; D010456:Peptides, Cyclic / Q000494:pharmacology*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism*; D012995:Solubility / Q000187:drug effects; D013500:Surface Tension / Q000187:drug effects; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D005742:Gasoline; D006017:Glycolipids; D055666:Lipopeptides; D010456:Peptides, Cyclic; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; C418382:rhamnolipid; C009365:surfactin peptide