Environmental Engineering Reference
In-Depth Information
Reprinted from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com) and WH Freeman (www.whfreeman.com), with permission.
Figure 1. Structure of cellulose as it occurs in a plant cell wall.
3. Bioreactors and Bioseparations
Similarly, reactor and separations technologies must play important roles in the
development of economically feasible biorefineries, as these processing steps often contribute
the greatest expense of the final products. At early stages of development, new
bioengineering processes often benefit greatly from combination of separate components. For
example, integrating unit operations, as into reactor-separators and other novel processes,
often provides immediate improvements in efficiency. Similarly, integrating individual
production steps into a multi-product biorefinery, and integrating biorefineries into the
broader economic and environmental systems in which they function, are important avenues
to economic feasibility. To evaluate energy, material, and cost efficiencies of these systems,
Life-cycle Analysis (LCA) tools are invaluable and are themselves undergoing rapid
development [23]. An enormous barrier exists in the funding and deployment of any pioneer
manufacturing plant, and federal programs may be necessary to provide loan guarantees and
other incentives to encourage enterprise in this direction [24].
Complete sustainability . Important considerations in the overall sustainability of both
biofuels and biomaterials include the fossil-energy costs of agriculture and processing. For
example, current practices of conventional agriculture use petroleum-powered machinery and
fertilizers synthesized with fossil energy. In addition, conventional processing techniques use
nonsustainable energy sources. Furthermore, the treatment of acidic, alkali, and/or organic
wastes resulting from processing techniques consumes additional energy. As a result, no
biofuel or biomaterial is currently completely sustainable as an energy resource or completely
free of pollution generation. Bioethanol, in particular, has come under criticism for its use of
intensively-cultivated food crops, while several bioplastics potentially use as much fossil
energy in their processing as petroplastics use in their feedstocks and processing combined.
For this reason, development of technologies that use waste or other biofeedstocks with low-
embodied energy (energy consumed in its production) is a high priority for both biofuels and
biomaterials as is development of efficient bioprocesses, including enzymatic and therefore
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