Technical Session 21: Spent Grains Session
Jason Bennett, University of Abertay, Dundee, Scotland UK
Co-author(s): Graeme Walker and David Bremner, University of Abertay, Dundee, Scotland
ABSTRACT: Bioethanol (fuel ethanol derived through
fermentation) is now the leading biofuel alternative to fossil-based
liquid transportation fuels. Current production is dominated by U.S.
corn-based and Brazilian sugarcane-based processes. However, more
sustainable future bioethanol production needs to be based on non-food
substrates that use lignocellulosic biowastes. The brewing and
distilling industry sectors are uniquely placed to exploit the
conversion of lignocellulose to bioethanol, through the utilization of
spent grains. Bioconversion of brewer’s spent grains (BSG) to fuel
alcohol represents an attractive but challenging opportunity for
sustainable bioethanol production. In addition to the technological and
scientific challenges in bioethanol production from spent grains, there
are also constraints relating to economics and energy balances. For
example, enzyme costs need to be lowered, particularly considering
cellulolysis of feedstock. Any innovations to decrease cellulase enzyme
dosage are a distinct advantage. We have evaluated the influence of
ultrasonic irradiation (at varying frequencies between 382 and 1,174
kHz) on cellulolytic enzymatic digestion of pre-treated BSG. Results
have shown that ultrasonic irradiation during enzymolysis increases the
total sugar release rate from BSG. In particular, results from exposure
of enzymolysis to ultrasound at a frequency of 998 kHz shows that
ultrasound holds the potential to significantly reduce the dosing rates
of cellulose enzyme required for the hydrolysis of lignocelluloses.
Different yeast species, including Saccharomyces cerevisiae, Pichia stipitis, Kluyveromyces marxianus, Pachysolen tannophilus, and Candida shehatae,
have been evaluated for their ability to ferment the mix of five and
six carbon sugars liberated following ultrasonic pretreatment and during
enzymatic hydrolysis of BSG. Results have indicated that while Saccharomyces cerevisiae can ferment hexose sugars within BSG hydrolysates, it lacks the ability to ferment pentose sugars. Pichia stipitis, Kluyveromyces marxianus, Pachysolen tannophilus, and Candida shehatae
exhibited the ability to ferment the full range of both hexose and
pentose sugars within BSG hydrolysates. However, sugar utilization
between species varied greatly, with Pichia stipitis and Kluyveromyces marxianus
displaying the best fermentation performance. Research conducted during
this study has shown that the application of ultrasonic technology
during the enzymolysis of BSG has the potential to significantly reduce
the costs associated with cellulolytic enzyme dosing during the
bioconversion of lignocellulosic substrates to bioethanol.
Jason
Bennett graduated with a B.S. degree in biotechnology from the
University of Abertay Dundee in 2008, with a thesis titled “The
Application of Ultrasound in Yeast Biotechnology.” He is currently
completing his Ph.D. degree with a thesis titled “The Application of
Ultrasound in Bioconversion of Brewer’s and Distiller’s Spent Grains to
Bioethanol.” In January 2012 he commenced a new post within the
university, focusing on developing sustainable solutions for dealing
with the co-products produced during malt whisky distillation.
VIEW PRESENTATION 72
