Evaluation of triticale straw as feedstock for the production of bioethanol in a SSF process

Kossatz, Hester Lalie (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: The production of renewable liquid fuels such as bioethanol is currently at the forefront of scientific research, with a specific focus on production processes that are sustainable, inexpensive and environmentally friendly. Traditional biofuel feedstocks include maize, wheat, sugar and sugar beet, which can be easily converted to ethanol using hydrolytic enzymes and microorganisms. The focus has recently shifted to less expensive feedstocks, namely lignocellulosic biomass. Lignocellulose is found in all plants and byproducts or waste material from several industries can therefore be utilised for the production of lignocellulosic bioethanol, including paper sludge, wood chips, corn stover, sugarcane bagasse and straw. One of the potential alternative feedstocks for bioethanol is triticale straw. Triticale (Triticosecale rimpau) is a robust and tolerant cereal crop that is cultivated worldwide and has desirable qualities such as disease and drought tolerance and the ability to grow on marginal land. It produces grain with high protein content suitable as food or animal feed, whereas the straw has little monetary value and is therefore an ideal feedstock for bioethanol production. The straw is more susceptible to enzymatic hydrolysis than other lignocellulosic sources such as wood, sugarcane bagasse and corncobs. However, little research has been done on the enzyme activities and dosages required to utilise triticale straw as bioethanol feedstock. In this study, triticale straw was evaluated using steam-explosion pretreatment, enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) as processing pipeline. The conditions for steam-explosion were set at 203°C for 7 minutes, which improved the cellulose content of the straw by 6% and reduced the hemicellulose content by 17%. One kilogram of triticale straw produced 720 grams of water-insoluble solids (WIS), as well as a liquid fraction. Five commercial cellulase cocktails were evaluated for the hydrolysis of the WIS, with Spezyme® CP delivering the highest glucose yield (57%) at 15 FPU/g cellulose. Several strains of Saccharomyces cerevisiae were screened for their fermentative ability at 37°C and high glucose concentrations and Ethanol Red®, an industrial strain, and the wild-type strain L21 were selected for evaluation in an SSF setup. The combination of 15 FPU/g Spezyme® CP and Ethanol Red® yielded the best results on the triticale WIS, with 26.9 g/l ethanol produced after 144 hours, corresponding to 92% of the theoretical ethanol yield. The promising performance of triticale straw under laboratory conditions therefore supports further investigation on an industrial scale.

AFRIKAANSE OPSOMMING: Die produksie van hernubare vloeibare brandstof, soos bio-etanol, is tans aan die voorpunt van wetenskaplike navorsing, met spesifieke fokus op produksieprosesse wat volhoubaar, goedkoop en omgewingsvriendelik is. Tradisionele bio-etanol voerstowwe sluit mielies, koring, suiker en suikerbeet in, wat maklik deur hidrolitiese ensieme en mikro-organismes na etanol omgeskakel kan word. Die fokus het onlangs na goedkoper voerstowwe, naamlik lignosellulosiese biomassa, verskuif. Lignosellulose word in alle plante gevind en neweprodukte of afvalmateriaal van verskeie nywerhede, insluitende papierslyk, hout splinters, mieliestronke, suikerrietbagasse en strooi kan dus vir die produksie van bio-etanol aangewend word. Een van die potensiële alternatiewe voerstowwe vir bio-etanol is korogstrooi. Korog (Triticosecale rimpau) is 'n geharde en verdraagsame graansoort wat wêreldwyd verbou word. Dit het verskeie gewensde eienskappe, insluitende siekte- en droogtebestandheid en die vermoë om op marginale grond te groei. Dit produseer graan met 'n hoë proteïeninhoud wat as voedsel of veevoer geskik is, terwyl die strooi min geldwaarde het en dus die ideale voermateriaal vir bio-etanolproduksie is. Strooi is meer vatbaar vir ensiematiese hidrolise as ander lignosellulosiese bronne soos hout, suikerriet bagasse en mieliestronke. Nietemin is min navorsing op die ensiemaktiwiteite en dosering vir die benutting van korogstrooi as voerstof vir bio-etanol gedoen. In hierdie studie word korogstrooi geëvalueer deur gebruik te maak van voorbehandeling met stoomontploffing, ensiematiese hidroliese en gelyktydige versuikering en fermentasie (GVF). Die toestande vir stoomontploffing was 203°C vir 7 minute, wat die sellulose-inhoud van die strooi met 6% verhoog en die hemisellulose-inhoud met 17% verminder het. Een kilogram korogstrooi het 720 gram totale onoplosbare vastestowwe (TOV) gelewer, asook ‘n vloeibare fraksie. Vyf kommersiële sellulasemengsels is vir die hidroliese van die TOV geëvalueer, waaronder Spezyme® CP die hoogste glukose-opbrengs (57%) met 15 FPU/g sellulose gelewer het. Verskeie stamme van Saccharomyces cerevisiae is vir hul fermentasievermoë by 37°C en hoë glukosekonsentrasies gesif en Ethanol Red®, ‘n industriële stam, sowel as die wilde-tipe L21 ras, is vir gebruik in ʼn GVF-opstelling gekies. Die kombinasie van 15 FPU/g Spezyme® CP en Ethanol Red® het die beste opbrengs gelewer, met 26.9 g/l etanol wat na 144 ure geproduseer is, gelykstaande aan 92% van die teoretiese etanolopbrengs. Die belowende prestasie van korog strooi onder laboratoriumtoestande ondersteun verdere ondersoek op 'n industriële skaal.

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