Multi-scale biosurfactant production and biosurfactant=aided soil washing

Hu, Jiheng (2022) Multi-scale biosurfactant production and biosurfactant=aided soil washing. Masters thesis, Memorial University of Newfoundland.

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Abstract

Biosurfactants are widely used in oil and environmental industries due to their unique properties. The thesis first focused on examining tuna fish waste as low-cost substrates for microbial growth through an enzyme hydrolyzation process to produce the biosurfactant, surfactin. After enzyme hydrolyzation, the biosurfactant fermentation experiments were conducted at the bench-scale, batch-scale, and pilot-scale to determine optimal conditions for potential industrial production operations. Tuna fish waste was demonstrated to be a feasible substrate for supporting the growth of Bacillus subtilis (ATCC® 21332™) for biosurfactant synthesis. Optimal parameters for surfactin production (274 mg/L) were determined by conduct of the multi-scale fermentation tests. The thesis also tackled evaluating the potential of biosurfactant-aided soil washing under different temperatures and salinity levels for oil removal. Rhamnolipids biosurfactant and Dioctyl sulfosuccinate sodium salt (DOSS) were mixed at several ratios in shaken flasks to conduct the research. Analysis of the surfactant and crude oil emulsions were developed based on their microscopic images and interfacial tension (IFT). The causal effect of IFT on crude oil removal efficiency was estimated by the structural causal model (SCM). Results of SCM showed that IFT has a minor suppression to the removal efficiency from an overall perspective but can enhance the removal efficiency under the high salinity. The findings of this thesis shed light on biosurfactant production using fish wastes as an economical substrate and biosurfactant-aided soil washing for solving shoreline oil pollution problems. The thesis also demonstrated the applicability of causal inference analysis in environmental engineering.

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