Masters Degrees (Microbiology)

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Browsing Masters Degrees (Microbiology) by Subject "Algal biofuels"

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    Microalgae as a feedstock for ethanol production
    (Stellenbosch : Stellenbosch University, 2023-12) De Villiers, Dewald; Van Zyl, Willem Heber; Viljoen-Bloom, Marinda; Cripwell, Rosemary Anne; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Microalgae are increasingly considered a source for high-value products in various markets, with applications in the health food, medicinal and industrial sectors. More recently, microalgae have gained interest as a feedstock for biofuel production due to their high starch content. Various studies investigated the challenges of using microalgae in industry, such as low biomass production, complicated harvesting methods and high lipid/carbohydrate content. Although solutions and mitigation strategies have been proposed, the process must be economically feasible to compete with fossil fuels and other biofuel feedstocks. This could be achieved by optimisation of the growth conditions to maximise the biomass and starch yields and/or through enzymatic treatment to release the starch for fermentation to bioethanol. In this study, the growth conditions for two microalgal strains known for their starch - producing capabilities, Chlamydomonas reinhardtii and Chlorella sorokiniana, were optimised for enhanced biomass and starch accumulation, specifically by evaluating different carbon and nitrogen sources. The two strains were grown under mixotrophic conditions, i.e. photosynthesis in the presence of additional carbon sources (glucose and acetic acid). The C. sorokiniana strain displayed the highest biomass production (3.89 g/L) and starch accumulation (0.67 g/L) when grown in Bold Basal Media (10 g/L glucose) with a modified carbon-to-nitrogen ratio (C:N of 8:1). The C. sorokiniana strain was evaluated in a consolidated bioprocessing (CBP) process for starch-ethanol fermentation by optimising the harvest methods and pretreatment options. The study found that enzymatic pretreatment coupled with freeze-drying provided the best results. The C. sorokiniana biomass was pretreated enzymatically with pectinase and xylanase to release the internal starch granules. Consolidated bioprocessing with an amylolytic Saccharomyces cerevisiae strain (co-expressing an α-amylase and glucoamylase) yielded 4.02 g/L ethanol from a 10% microalgal substrate loading at 30°C. This study is one of only a few that observed microalgae growth in a standardised, mixotrophic growth setting where macronutrients were evaluated for optimised starch production.