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Oral Presentation 3-07 Conversion of Paper Sludge
to Ethanol in a Novel Semi-Continuous Solids-fed Reactor System Capable of
Metered Aseptic Delivery of Solid Substrates
Zhiliang Fan1, Colin South3,
Kimberly Lyford4, Jeffery Munsie5, Mateusz M. Nowak,1
Peter van Walsum6, and Lee R. Lynd
1,2
1Chemical and Biochemical Engineering Program Thayer School of Engineering 8000 Cummings Hall Hanover, NH 03755
2Department of Biology Dartmouth College Hanover, NH
03755
3Biometics
Waltham, MA Telephone: (603) 643-7784; Fax (603) 646-3856; E-mail: Zhiliang.Fan@Dartmouth.Edu
Paper
sludge is the largest solid waste stream produced by the pulp and paper
industry. We describe results obtained
in a novel solids-fed laboratory-scale bioreactor system capable of aseptic,
semi-continuous metered delivery of paper sludge. Results using this system are presented for a simultaneous
saccharification and fermentation system in which cellulose hydrolysis is
mediated by exogenously added cellulase and fermentation to ethanol is mediated
by Saccharomyces cerevisiae. These include compositional analysis,
reactor design modifications to improve reliability, production of recoverable
ethanol concentrations, operation for periods up to 5 months, steady-state
material balances, and economic analysis.
Modification of standard analysis techniques was found to be necessary
in order to compensate for the alkalinity of paper sludges, and in particular
to avoid underestimating sludge cellulose composition. Modification of the reactor design was
necessary to improve reliability and avoid solids accumulation. With these analytical and reactor
modifications, steady-state operation was obtained under conditions that meet
many threshold values for economic operation: ethanol concentration ≥ 40
g/L, cellulose conversion
≥ 90% of theoretical, reaction time 4 days. The cellulase loading used was, however,
higher than likely in a commercial process at 20 IU/g cellulose with
supplemental
b-glucosidase. Paper sludge is
an unusual cellulosic feedstock because many sludges are highly amenable to
enzymatic hydrolysis without a dedicated pretreatment step and because
significant disposal costs can be avoided by converting sludge to ethanol or other
value-added products. Largely because
of these factors, economic models show potential for attractive returns at a
production scale and capital investment much lower than possible for more
typical feedstocks. Our results suggest
that paper sludge is an attractive point-of-entry and proving ground for
emergent industrial processes featuring enzymatic hydrolysis of cellulosic
feedstocks.
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