Environmental Engineering Reference
In-Depth Information
and other toxic compounds. Together with increasing ethanol concentrations, this
can inhibit the enzymes and fermentation organisms, thus lowering yields. New
developments in enzymatic saccharification and fermentation have been developed
by Iogen Energy Corporation and the NREL to develop effective “cocktails” of
enzymes along with modified strains of yeast that can break down complex sugar
molecules, which conventional fermentation yeast cannot.
Recently, Royal Dutch Shell (Shell) announced a partnership with Iogen Energy
Corporation to advance cellulosic ethanol from agriculture residues such as cereal
straw and corn cobs and stalks. And just recently, Iogen Energy shipped 100,000 L
(26,417 gal) to Shell, which is the first installment of the initial order of 180,000 L
(47,550 gal) of cellulosic ethanol. Iogen's demonstration facility located in Ottawa,
which first began producing cellulosic ethanol in 2004, is being purchased by Shell
for use in upcoming fuel applications [59].
Cellulolytic microorganisms, an alternative to yeast, utilize ethanol fermenting
microbes that both hydrolyze and ferment the sugars into ethanol from a milder
pretreatment process. Gram-negative bacteria, such as
Escherichia coli
,
Klebsiella
oxytoca
, and
Zymomonas mobilis
, are being investigated as potential microor-
ganisms for industrial production of ethanol [52]. Using genetic and metabolic
engineering, NREL has developed a strain of
Z. mobilis
(Zymo) that can break
down complex sugars like xylose, and tolerate higher concentrations of acetic acid
[51]. Other studies have shown that the
Z. mobilis
strain can produce theoretical
yields up to 95% and handle a wider range of feedstocks [52]. High technological
costs have impeded the widespread production of cellulosic ethanol by microor-
ganisms. Consolidated bio-processing or CBP has been developed to address this
problem. This process utilizes cellulolytic microorganisms to perform the hydroly-
sis of biomass and the fermentation of sugars into ethanol within a single process,
which is a large cost reducing strategy [53]. CBP is expected to reduce overall
production costs by eight-fold compared to SSF under similar conditions.
Mascoma Corporation has dedicated their research team to focus on the com-
mercialization of CBP, which is seen as the lowest cost configuration for cellulosic
ethanol. Mascoma Corporation is in the process of developing a cellulosic fuel pro-
duction facility that will use non-food biomass to convert woodchips into fuel. They
are predicting that the new facility will produce 40 million gallons of ethanol and
other valuable fuel products per year [60].
4.3 Summary
Cellulosic ethanol is ethyl alcohol produced from wood, grass, or the non-edible
parts of plants, and is a sustainable and renewable biofuel that is biodegradable.
The promising features of cellulosic ethanol are the diverse and abundant feedstock
that can utilize existing waste by-products. Iogen Energy Corporation is currently
producing cellulosic ethanol for Shell using enzymatic saccharification and fermen-
tation in a small-scale commercial facility. Another approach to cellulosic ethanol
is via the use of cellulolytic microorganisms. As commercialization of cellulosic
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