Generation of biodispersants for offshore oil spill response

Cao, Tong (2015) Generation of biodispersants for offshore oil spill response. Masters thesis, Memorial University of Newfoundland.

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Abstract

Biodispersants are detergent-like products made by dissolving biosurfactants in solvents. Biosurfactants, comparing with their chemical counterparts, have advantages of lower eco-toxicity, as well as higher biodegradability and stability. Biodispersants have the great potential to be applied as the reagent for offshore oil spill response. However, relevant topics were rarely reported in literature due to the extremely limited biodispersants available and the high cost of biosurfactant production. This study thus tried to fill the research gap through enhancing the producting of biosurfactants so as to decrease the cost and generating biodispersant products for oil spill response. The biosurfactants were produced by Rhodococcus erythropolis sp. SB-1A, a strain isolated from the North Atlantic Ocean. Effects of culturing conditions including the carbon source, the nitrogen source, pH and salinity were investigated through the One-factor-at-a-time (OFAT) experiments. Surface tension and the reciprocal of critical micelle concentration (CMC-1) of the cell-free culture were monitored periodically. A kinetics model was established to represent the time course of biosurfactant production. Under the determined culturing conditions (3.5 v/v% N-hexadecane, 0.7 g/L NH4NO3, pH 7 and 26 g/L NaCl), the surface tension of culture mediums was reduced by 40 dynes/cm with a CMC-1 of 11.9 after 40 hours of cultivation. The produced biosurfactants were further characterized. Results indicated that the total carbohydrate content in 1 g of biosurfactants was 8.4 mg in term of D-glucose, and the total lipid content in 1 g of biosurfactants was 11.6 mg in term of Palmitic acid. Multiple solvents were selected to mixed with the biosurfactants, respectively, to obtain the biodispersants. The solvents were screened based on their toxicity and the effectiveness of relevant dispersants generated. The final formula of the biodispersant was determined as 16.7%/ 83.3% (biosurfactants/ PEG 400). The biodispersant-based dispersion was further examined using a motor oil sample and a crude oil sample. The performance was compared with the commercial chemical dispersant Corexit 9527. Results showed that compared with Corexit 9527, the biodispersant could achieve a compatible dispersant effectiveness (DE) when treating the motor oil and a higher DE for treating the crude oil. Through the biodegradation test, 45% of the biodispersed crude oil was biodegraded by the biodispersant assisted dispersion after 28 days of dispersion treatment without spiking any oil-degrading bacteria. The toxicity of the biodispersed oil was reduced by 50% after 28 days. The research outputs provided an evidence for applying biodispersants as a promising alternative reagent for offshore oil spill response.

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