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Biomass, Bioengineering of 155

other bases, pressurized hot water and catalytic amounts volume of such byproducts can be very large and there is
of acid. Such pretreatments may eventually make it pos- a pressing need to find markets for all such products and
sible to convert a large array of lignocellulose residues byproducts.
into useful products. It has long been recognized that a Bioprocessingresearchshouldthereforefocuson(1)in-
technologically and economically successful lignocellu- creasing processing rates to reduce the capital investment
lose pretreatment will not only unlock the sugars in plant required, (2) increasing product yields to decrease the raw
material for conversion to industrial products but will also material costs and to reduce the load on the separation
make these sugars more available for animal feeding. and waste disposal systems, and (3) increasing product
Considerable progress has been made in developing ge- concentrations to reduce separation costs. One drawback
netically engineered microorganisms that can utilize the is that bioprocesses typically yield dilute aqueous prod-
completerangeofsugarsinlingocellulosicmaterials.Both uct streams that require further processing to separate
genetically engineered bacteria and yeasts are now avail- and purify products. Separation technologies for biobased
able that utilize both five and six carbon sugars and con- products are typically less developed than separation tech-
vert them to ethanol. However, less progress is apparent in nologies for comparable petroleum-based products. A ma-
production of low cost cellulase enzymes, an active area jor need is to find low cost ways of removing the large
of development at this time. Fortunately, while research amounts of water that often accompany biobased prod-
on cellulases will take both time and money, the research ucts. In general, research on the underlying production
pathways required to achieve success, (i.e., much lower processes should focus on the science and engineering re-
cost active cellulases), are relatively clear. quired to overcome the most significant cost barriers to
It may also be possible to largely bypass the processes commercializing biobased products.
of cellulose pretreatment and enzymatic hydrolysis to pro- Experience with commercial amino acid production il-
duce fermentable sugars. One such approach is to gasify lustrates the potential of combining inexpensive raw ma-
biomass to mixtures of carbon dioxide, hydrogen and terials with advanced processing technologies. Interna-
carbon monoxide and then to ferment the resulting gas tional amino acid markets were completely dominated by
mixture to ethanol or other products. This amounts to a Japanese firms in the early 1980s. However, in the 1990s
technological “end run” around the processes of biomass U.S. companies used inexpensive corn-based sugars and
pretreatmentandenzymatichydrolysis,andcouldalsosig- an advanced processing method, immobilized cell tech-
nificantly simplify the fermentation process. Two major nology, to penetrate these markets and now occupy a sig-
technical obstacles to this approach include clean up of nificant part of the global amino acid trade.
the gas stream, particularly to remove sulfur and nitrogen- One of the reasons these corn-based sugars for amino
containing compounds, and also the difficulty of trans- acid production were so inexpensive is because they were
ferring slightly soluble gases into a liquid fermentation produced in large, integrated biorefineries. The Archer
mixture. DanielsMidlandplantinDecatur,Illinois,isaprototypical
biorefinery. At that location, a large corn wet-milling plant
and a steam and electricity cogeneration station burning
3. Generic Biomass Processing Technologies
wastetiresformthenucleusforseveralotherplantsthatare
The following comments apply generally to biomass con- highly integrated. These other plants are an ethanol facility
version, not just to lignocellulose conversion. Processing as well as an amino acid production plant. Biorefineries,
technologies that utilize microbes and enzymes have great whether based on corn, straw or any other material, must
potential for low cost biomass processing. Unlike most aspire to a similar degree of integration and effectiveness
thermal and chemical processes, bioprocesses take place in raw material conversion.
under relatively mild conditions of temperature and pres-
sure. Higher temperatures and pressures add significantly
to the cost of processing in conventional chemical indus- V. POTENTIAL AND LIMITATIONS
tries so that advanced bioprocessing technologies have OF BIOMASS AND BIOBASED
the potential to be less expensive than their non biological
INDUSTRIAL PRODUCTS
counterparts. Some advanced bioprocessing technologies
utilizing microbes and enzymes have already been de-
A. Potential Benefits
veloped, for example, immobilized cell technology and
simultaneous hydrolysis and fermentation of sugars from Biomass production and processing have the potential to
lignocellulosics. Bioprocesses result in stereospecific con- give us a uniquely sustainable source of organic chemi-
versions (the particular arrangement of atoms in space) cals, organic materials (such as biopolymers) and liquid
and produce relatively nontoxic byproducts. However, the transportation fuels. Biomass can also help us sustainably