Environmental Engineering Reference
In-Depth Information
Table 1.3
Biosorption of U(VI) by bacterial cells
Cellular structures
Descriptions
Sites for U(IV)
immobilization
References
Cell Wall
S-layer
Part of cell envelope commonly
found in bacteria. It consists
of identical protein or
glycoprotein subunits. It is
5-15 nm thick with pores
2-6 nm in diameter
Carboxylate and
phosphate
groups
[140]
Peptidoglycan Thick layer of 25 nm in
Gram-positive bacteria and
thin layer of 4 nm in
Gram-negative bacteria
Carboxylate and
phosphate
groups
[141, 142,
143]
Outer
membrane
Outer membrane bilayer
consisting of
lipopolysaccharide (LPS) and
protein outside the
peptidoglycan layer in
Gram-negative bacteria
Carboxylate and
phosphate
groups
[144, 145]
Extracellular polymeric
substances (EPS)
Molecules from metabolism,
organic effluents, and
microbial lysis, including
polysaccharides, proteins,
humic substances, uronic
acids, nucleic acids and lipids
Carboxylate,
phosphate,
amine, and
hydroxyl
groups
[146, 147]
intracellular uptake results from increased cell membrane permeability caused, for
example, by the toxic effects of uranium.
1.2.2.2 Bioremediation Principles: From the Laboratory to the Field
Although the underlying principles of uranium bioremediation have been exten-
sively studied using model systems (pure cultures) and proof-of-concept systems
(laboratory studies of natural soils and sediments containing mixed microbial com-
munities) [57, 58, 59], practical field-scale studies have only been carried out more
recently [44]. Theoretically, both the immobilization of uranium in place (preventing
further downgradient spreading of groundwater contamination) and its mobilization
(allowing it to be more easily flushed) present opportunities for uranium bioremedi-
ation. Hazen and Tabak [32] suggested that mobilization can be a better long-term
strategy because it provides a way to remove the contaminant from solid matrices,
such as soils, sediments, dumps and other solid industrial wastes. However, it is
difficult to justify to regulators and stakeholders at remediation sites because of its
inherently greater risk if the mobile and usually more toxic contaminant fails to
be adequately immobilized in the capture zone. Therefore, in uranium bioremedi-
ation, almost all of the reported field studies and deployments to date have used
immobilization rather than remobilization.
