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Production of Ethanol and Biomass from Thin Stillage Using Food-Grade Zygomycetes and Ascomycetes Filamentous Fungi
University of Borås, School of Engineering. (Biotechnology)
University of Borås, School of Engineering. (Biotechnology)
University of Borås, School of Engineering. (Biotechnology)ORCID iD: 0000-0003-4887-2433
2014 (English)In: Energies, Vol. 7, no 6, p. 3872-3885Article in journal (Refereed)
Sustainable development
The content falls within the scope of Sustainable Development
Abstract [en]

A starch-based ethanol facility producing 200,000 m3 ethanol/year also produces ca. 2 million m3 thin stillage, which can be used to improve the entire process. In this work, five food-grade filamentous fungi, including a Zygomycete and four Ascomycetes were successfully grown in thin stillage containing 9% solids. Cultivation with Neurospora intermedia led to the production of ca. 16 g·L−1 biomass containing 56% (w/w) crude protein, a reduction of 34% of the total solids, and 5 g·L−1 additional ethanol. In an industrial ethanol production process (200,000 m3 ethanol/year), this can potentially lead to the production of 11,000 m3 extra ethanol per year. Cultivation with Aspergillus oryzae resulted in 19 g·L−1 biomass containing 48% (w/w) crude protein and the highest reduction of the thin stillage glycerol (54%) among the Ascomycetes. Cultivation with Rhizopus sp. produced up to 15 g·L−1 biomass containing 55% (w/w) crude protein. The spent thin stillage had been reduced up to 85%, 68% and 21% regarding lactic acid, glycerol and total solids, respectively. Therefore, N. intermedia, in particular, has a high potential to improve the ethanol process via production of additional ethanol and high-quality biomass, which can be considered for animal feed applications such as for fish feed.

Place, publisher, year, edition, pages
MDPI , 2014. Vol. 7, no 6, p. 3872-3885
Keyword [en]
Resource Recovery
National Category
Industrial Biotechnology
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-1871DOI: 10.3390/en7063872ISI: 000338557600022Local ID: 2320/13764OAI: oai:DiVA.org:hb-1871DiVA: diva2:869949
Available from: 2015-11-13 Created: 2015-11-13 Last updated: 2016-03-03
In thesis
1. Integration of filamentous fungi in ethanol dry-mill biorefinery
Open this publication in new window or tab >>Integration of filamentous fungi in ethanol dry-mill biorefinery
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The industrial production of bioethanol as a replacement to gasoline is well-established worldwide, using starch- or sugar-rich substrates. Additionally, the bioethanol plants produce animal feeds derived from fermentation leftovers. The biorefinery character of bioethanol plants can be enhanced via process diversification. This entails the production of more value-added products, which can be accomplished by including edible filamentous fungi as the second biocatalysts while taking advantage of the available equipment for cost-effective inclusion. The process diversification can be achieved either via valorisation of the process leftovers or via inclusion of other residual substrates.

 

In dry-mill biorefineries, baker’s yeast is unable to consume residual pentose sugars and other more complex substrates in the process leftovers so called whole stillage and thin stillage. Edible ascomycetes and zygomycetes fungi can be used to accomplish yeast and consume those residual substrates in stillage as well as from external substrates of lignocellulosic origin, e.g. spent sulphite liquor and wheat straw. The conversion of these substrates to ethanol, and biomass rich in protein, lipids, respective essential amino acids and fatty acids as well as chitosan was investigated in this thesis.

 

Among the filamentous fungi studied, Neurospora intermedia was the best ethanol producer from thin stillage. Process developments included primary shake-flasks experiments, followed by pilot scale-up using 26 L, 2.3 m3 and 80 m3 bioreactors. The 26 L bioreactor, as a bubble column led to similar performance as an airlift bioreactor, and also a continuous mode could be successfully used instead of a batch process. By using a dilution rate of 0.1 h-1, around 5 g/L of ethanol and 4 g/L of biomass rich in protein, lipids, amino acids and fatty acids essential to humans were obtained. The inclusion of the process can potentially lead to a spent medium lower in solids and viscosity which may facilitate the energy-intensive evaporation and drying steps as well as the water recycling back to the process. By applying a two-stage cultivation with whole stillage, up to 7.6 g/L of ethanol could be produced using 1 FPU cellulase/g suspended solids and 5.8 g/L of biomass containing 42% (w/w) crude protein. In the first stage (ethanol production), N. intermedia was used, while Aspergillus oryzae was the biocatalyst in the second stage for further biomass production. Both strains were able to degrade complex substrates both in liquid and solid fraction of whole stillage. The extrinsic substrates included spent sulphite liquor and pretreated wheat straw slurry. When the former was used, up to around 7 g/L of Rhizopus sp. could be obtained in a 26 L airlift bioreactor. The biomass was rich in protein and lipids (30–50% and 2–7% on a dry weight basis, respectively). The monomers of the latter were continuously filtered for production of biomass under simultaneous saccharification fermentation and filtration. Biomass yields of up to 0.34 g/g of consumed monomeric sugars and acetic acid were obtained.

 

The inclusion of the process for valorisation of thin stillage can potentially lead to the production of 11,000 m3 ethanol and 6,300 tonnes of biomass at a typical facility producing 200,000 m3 ethanol/year.

Place, publisher, year, edition, pages
Borås: Högskolan i Borås, 2015. p. 96
Series
Skrifter från Högskolan i Borås, ISSN 0280-381X ; 73
Keyword
airlift bioreactors, ascomycetes, biomass, bubble column, ethanol, feed, Neurospora intermedia, thin stillage, zygomycetes
National Category
Environmental Biotechnology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-674 (URN)978-91-87525-77-3 (ISBN)978-91-87525-78-0 (ISBN)
Public defence
2015-11-13, E310, Allégatan, Borås, 10:00 (English)
Available from: 2015-10-20 Created: 2015-08-27 Last updated: 2015-12-18Bibliographically approved

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