Biosurfactant enhanced soil bioremediation and associated microbial community analysis

Li, Xixi (2018) Biosurfactant enhanced soil bioremediation and associated microbial community analysis. Masters thesis, Memorial University of Newfoundland.

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Abstract

The nutrient and rhamnolipid biosurfactant enhanced soil bioremediation of petroleum hydrocarbons (PHCs) and the associated microbial communities were investigated in this thesis. A systematic factorial design was conducted, and a response surface reduced quadratic model was developed to determine the effects of the nutrients and two surfactants (i.e., rhamnolipids and Tween 80) in the degradation of PHCs within 36 days. A significant effect as a result of nutrient addition and a 92.3% removal of PHCs was achieved by applying rhamnolipids at a concentration of 150 mg/kg and a 1000 μL nutrient solution in every 30 g of soil. Rhamnolipids resulted in higher metabolic activities of indigenous soil microorganisms to assimilate hydrocarbons than Tween 80 based on kinetic investigation. Using phospholipid fatty acid (PLFA) analysis, three different total biomass transformation patterns were observed when the soils were treated by natural attenuation, by rhamnolipid aided bioremediation or Tween 80 aided bioremediation, respectively. As indicated by PLFA biomarkers of the Gram-negative bacterial populations (cy17:0, cy19:0, 16:1ω7c and 18:1ω7c), Gram-negative bacteria are closely correlated with the total amount of soil biomass and are the sources of hydrocarbon-degrading microorganisms. The physiological status of the indigenous microorganisms was also evaluated using PLFA compositional characteristics to indicate environmental stress and elucidate biodegradation mechanisms linked to different soil treatments.

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