Electronic Thesis and Dissertation Repository

Thesis Format



Master of Engineering Science


Chemical and Biochemical Engineering


Rehmann, Lars

2nd Supervisor

Pjontek, Dominic



The production of biosurfactants is a more environmentally conscious and sustainable approach compared to petrochemical-derived surfactants. One of the main disadvantages preventing commercialization of biosurfactants is their high production costs. To improve process efficiency by increasing productivity, process modifications with a nitrogen enriched media and operating temperatures were explored. Fermentation conditions of 25°C, 800 rpm, pH of 3.5, and an aeration of 5.6 L/min, were used to evaluate the consistency of yields and productivity. At 25°C, the nitrogen rich fermentation encountered challenges maintaining dissolved oxygen (DO) >30%. This was overcome by operating at a lower temperature of 20°C during the growth phase of the cells. Nitrogen rich conditions of 20°C<24h, 25°C>24h yielded a biosurfactant productivity of 1.53 g/ L h which was 194% higher and 3 times more productive than baseline conditions. Further optimization of nitrogen rich media is suggested to balance cellular growth and product formation.

Summary for Lay Audience

The raw materials commonly used for detergent production are derived from petrochemicals. The rapid depletion of petroleum will impede synthetic surfactant production, and focus will be shifted to more bio-based surfactant options which are more biodegradable. Sophorolipids are a type of biosurfactant primarily produced by the yeast strain, Candida bombicola. They have become an ideal choice of biosurfactant due to their high production concentrations, making it an attractive option for an industrial scale-up. The fermentation process uses glucose and canola oil as the hydrophilic and lipophilic substrates respectively. A few factors that contribute to the high cost of sophorolipid production are fermentation time, yield, downstream processing, and energy requirements, which limit the commercial availability.

This thesis explores the use of nitrogen rich media and fermentation temperature as possible avenues for improving biosurfactant productivity. By increasing cell density during the growth phase, the fermentation time was reduced due to a greater number of cells available for product formation. However, the yield is impacted due to an increased oxygen demand during the growth phase. By operating at a reduced temperature during the growth phase, the productivity of the baseline fermentation was improved by 3-folds using a nitrogen rich media. Further exploration of the effects of nitrogen in the growth media is suggested, as a more refined balance may be achievable between sufficient cellular growth and product production phase.

Available for download on Tuesday, December 31, 2024