Microalgae as a feedstock for ethanol production

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dc.contributor.advisorVan Zyl, Willem Heberen_ZA
dc.contributor.advisorViljoen-Bloom, Marindaen_ZA
dc.contributor.advisorCripwell, Rosemary Anneen_ZA
dc.contributor.authorDe Villiers, Dewalden_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Microbiology.en_ZA
dc.date.accessioned2023-07-21T12:52:46Z
dc.date.accessioned2024-01-08T11:13:46Z
dc.date.available2023-07-21T12:52:46Z
dc.date.available2024-01-08T11:13:46Z
dc.date.issued2023-12
dc.descriptionThesis (MSc)--Stellenbosch University, 2023. en_ZA
dc.description.abstractENGLISH 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.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Mikroalge word toenemend as ‘ʼn bron vir hoëwaardeprodukte in verskeie markte beskou, met toepassings in die gesondheidsvoedsel, medisinale en industriële sektore. Meer onlangs het mikroalge belangstelling as grondstof vir biobrandstofproduksie geniet weens hul hoë styselinhoud. Verskeie studies het die uitdagings vir die gebruik van mikroalge in die industrie ondersoek, soos lae biomassaproduksie, uitdagende oesmetodes en hoë lipied-/koolhidraat- inhoud. Alhoewel oplossings en versagtingstrategieë voorgestel is, moet die proses ekonomies lewensvatbaar wees om met fossielbrandstowwe en ander biobrandstofgrondstowwe te kompeteer. Dit kan moontlik bereik word deur optimisering van die groeitoestande om die biomassa en styselopbrengste te maksimeer, en/of deur ensiematiese behandeling om die stysel vir fermentasie na bio-etanol vry te stel. In hierdie studie is die groeitoestande vir twee mikroalgrasse bekend vir hul styselproduserende vermoëns, Chlamydomonas reinhardtii en Chlorella sorokiniana, geoptimiseer vir beter biomassa en styselakkumulasie, spesifiek deur verskillende koolstof- en stikstofbronne te evalueer. Die twee rasse is onder miksotrofiese toestande gekweek, m.a.w. fotosintese in die teenwoordigheid van addisionele koolstofbronne (glukose en asynsuur). Die C. Sorokiniana-ras het die hoogste biomassaproduksie (3,89 g/L) en styselakkumulasie (0,67 g/L) getoon wanneer dit in Bold Basal Media (10 g/L glukose) met‘'n gewysigde koolstof-tot-stikstof-verhouding (C: N van 8:1) gekweek is. Die C. sorokiniana ras is in‘'n gekonsolideerde bioverwerking (CBP) proses vir stysel-etanol fermentasie ge-evalueer deur die oesmetodes en voorbehandelingsopsies te optimiseer. Die studie het bevind dat die kombinasie van ensiematiese voorbehandeling en vriesdroging die beste resultate gelewer het. Die C. sorokiniana biomassa is ensiematies met pektinase en xilanase behandel om die interne styselkorrels vry te stel. Gekonsolideerde bioprosessering met behulp van‘'n amylolitiese Saccharomyces cerevisiae-stam (wat beide α-amilase en glukoamilase uitdruk) het 4.02 g/L etanol vanaf ʼn 10% mikroalg-substraatlading by 30°C gelewer. Hierdie studie is een van slegs 'n paar wat die groei van mikroalge in 'n gestandaardiseerde, miksotrofiese groei-omgewing waargeneem het waar makrovoedingstowwe vir geoptimiseerde styselproduksie ondersoek is.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentv, 64 pages : illustrations (some color)en_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/128789
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshMicroalgae -- Growthen_ZA
dc.subject.lcshBiomass energyen_ZA
dc.subject.lcshMicroalgae -- Effect of stress onen_ZA
dc.subject.lcshAlgal biofuelsen_ZA
dc.subject.lcshMicroalgae -- Nitrogen content.en_ZA
dc.subject.lcshFeedstock -- Economic aspectsen_ZA
dc.subject.lcshChlamydomonas reinhardtii -- Effect of stress onen_ZA
dc.subject.lcshEthanolen_ZA
dc.subject.lcshChlorella sorokiniana -- Biotechnologyen_ZA
dc.subject.lcshStarchen_ZA
dc.subject.nameUCTDen_ZA
dc.titleMicroalgae as a feedstock for ethanol productionen_ZA
dc.typeThesisen_ZA
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