(529c) Evaluation of Non-Growth Biokinetic Models for Chromate Reduction with Shewanellae

                Hexavalent chromium is a carcinogenic pollutant often
associated with leather tanning and electroplating industries. Additional
applications have included its use as a corrosion inhibitor in cooling water
and as a colorant in dye and pigment compounds. Its widespread use in
industrial application has often been met with poor waste management practices,
leading to its release into the natural environment.

                Bioremediation has been proposed as a viable remediation
tool to reduce hexavalent chromium to its trivalent state. The rationale behind
this approach is that while the hexavalent form is very soluble and mobile in
the environment, the trivalent form is known to form insoluble precipitates
under most environmental conditions. Such a transformation results in chromium immobility.
Moreover, by utilizing microbes encountered in the subsurface environment, the
potential of designing an in situ treatment approach is much more
appealing when compared to more invasive ex situ approaches.

                In particular, Shewanella species have been
proposed as model organisms capable of hexavalent chromium reduction. The
widespread abundance of Shewanella in nature combined with the breadth
of genomic and physiological knowledge make it an ideal organism to study in
order to understand mechanisms of chromium reduction in the environment. To
this end, several Shewanella species were evaluated for their ability to
reduce chromium under anaerobic conditions in batch reactors.

                Data generated from these experiments was used to
estimate biokinetic parameters for models proposed in literature for remediation
of other types of pollutants. In this manner, we have evaluated the application
of these models for hexavalent chromium reduction. A ?transformation capacity? model
was selected based on its agreement with experimental data. Furthermore, the
sensitivity of this model to changes in biokinetic parameters was determined,
as well as the effects of pH, temperature, and electron donor. The data generated
from these studies suggests that biomass, pH, and electron donor are among the key
parameters to consider when using designing bioremediation based treatment
systems.