Environmental Engineering Reference
In-Depth Information
3.1. Membrane Techniques
The development of new and/or improved membrane materials that provide increased
selectivity and specificity for the desired substances, as well as increased flux with stability
and robustness, is of central importance to the membrane-based techniques discussed below
[5].
3.1.1. Pervaporation
. The use of pervaporation to remove either water or bioproducts
from bioreactor media appears promising. Continued support for new membrane materials,
new module and process designs, and improved theoretical understanding and modeling of
the pervaporation process should therefore be pursued. The work of Vane and colleagues at
the EPA National Risk Management Research Laboratory (NRMRL) is a noteworthy
example of efforts in the development of pervaporation modeling and performance prediction
software [30].
3.1.2. Micro- and ultrafiltration
. Microfiltration and ultrafiltration promise to become
major unit operations in the emerging biorefinery arena. The development of new materials
for UF and MF, including porous metals and ceramics as well as polymers, is therefore an
important priority. Similarly, nanofiltration and reverse osmosis are becoming increasingly
important, with recent developments in nanotechnology promising to yield new materials
with significantly improved fluxes and selectivities [5].
3.1.3. Membrane chromatography
. An improved understanding of the interactions
between culture media components and synthetic polymers suitable for membranes would
greatly facilitate the design of synthetic substrates for use in membrane chromatography.
Among those, ligand-binding and sterically-interacting species should be investigated closely
to improve the selectivity of membrane chromatography while maintaining acceptably high
throughput
3.1.4. Antifouling techniques
. Fouling is a persistent problem among membrane
technologies, with the result that methods to diminish fouling of membranes and ion
exchange materials, as well as to remove impurities such as salts or acids that cause
complications in downstream processes, are high priorities in the advancement of
bioseparations.
3.2. Environmentally Benign Solvents
New renewable, biodegradable solvents are needed to support environmentally-friendly
extraction processes. Supercritical CO
2
, a highly compressed phase of CO
2
possessing
properties of both liquid and gas phases, is one benign solvent that has already achieved great
popularity and that has the potential to contribute performance, cost-effectiveness, and
sustainability to separations of both biofuels and biomaterials [31].
3.3. Integrated Modules
Combined- or hybrid-unit operations in which a bioreactor is integrated with a
bioseparation module, as in two-phase reactor systems, are particularly attractive as means to
overcome limitations inherent to bioprocessing. These are particularly desirable for their
potential to remove products as they are synthesized, alleviating the nearly universal problem
of product inhibition in culture media [5].
