Environmental Engineering Reference
In-Depth Information
MgO/X2 (made by following the aerogel procedure) NPs have positive ^-potentials (e.g.,
27.0 mV for AP-MgO/Br 2 , 33.0 mV for AP-MgO/Cl 2 , and 35.2 mV for AP-MgO at 0.01
ionic strength NaCl) (Stoimenov et al., 2002). These NPs can tightly bind with the
bacteria surface because the overall charge of the bacteria and spore cells at biological
pH values is negative (Baszkin and Norde, 2000). As a result, bacteria and NPs form
aggregates (Stoimenov et al., 2002). On the other hand, bacterial cell walls and
envelopes as well as the walls of fungi, yeasts, and algae are efficient biosorbents that
bind charged groups. Cell membranes are mainly composed of polysaccharides, proteins
and hydrophobic lipid (bilayers) and have abundant binding groups such as carboxyl,
sulfate, phosphate and amino groups. The polysaccharides associated with microbial
cell walls allow exchange of bivalent metal ions for the counter ions of the
polysaccharides (Kuyucak and Volesky, 1988), resulting in the biosorptive uptake of
heavy metals that may be released by the NMs.
Table 15.7 Selected processes for possible biotransformation of NMs and contaminants
in different aquatic environments (Bollag and Liu, 1990; Bhandari et al., 2007) a .
Process Goal
NMs/Contaminants
4 kinds of NMs b ; metals
and radionuclides;
inorganic and organic
compounds
Temporarily or permanently
immobilizing NMs and contaminants
• Complexation
Biotransformation For mineralization:
• Mineralization
4 kinds of NMs; metals
and radionuclides;
inorganic and organic
compounds
Permanently immobilizing
NMs/contaminants;
• Detoxification
transforming them to CC>2, H 2 O and
other end products
• Cometabolism For the other 4 mechanisms/processes:
Change in NMs'/contaminant structure
to a more or less toxic end product
Bioaccumulation/ Contaminant extraction and accumulation
4 kinds of NMs; metals
and radionuclides;
recalcitrant organic
compounds with a high
K o w
a media: soils, porous media, ground and surface waters, wastewaters, sludge, biofilms, root
zones, sediments, etc. b Four kinds of NMs (USEPA, 2007): (a) Carbon-based NMs such as
fullerenes (spherical and ellipsoidal carbon NMs), nanotubes (cylindrical ones); (b) metal-based
NMs such as n-ZVI, metal oxide NPs; (c) dendrimers (nanoscale branched polymers that are
grown in a stepwise fashion); and (d) composites (combination of NPs and other NPs or larger,
bulk-type materials).
from
media to microbes, plants, animals,
and humans
Removal of NM from solution can also occur through complex formation with
amino and carboxyl groups found in cell wall polysaccharides.
In addition, the
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