Environmental Engineering Reference
In-Depth Information
enzymatic activity for the selective oxidation of sulfur in diesel fuel and to produce a
water-soluble sulfate salt, leaving the heterocyclic compound in the organic phase, thus
minimizing the loss of diesel fuel.
Petroleum contains between 0.1 and 2% nitrogen, with most crude oils
containing less than 0.3%. The three major groups of nitrogen compounds in petroleum
are pyridine derivatives (including quinolines and phenanthridines), indole derivatives
(including pyrroles, carbazoles, and benzocarbazoles), and aromatic amides. Many
authors have reported that isolate procaryotes are capable of degrading nitrogen
heterocycles. For example, Bacillus sp. and Nocardia sp. can utilize pyridine as a sole
carbon, nitrogen, and energy source (Watson et al., 1975). Quinoline served as the sole
carbon source when ammonium was present as a nitrogen source for a bacterium
isolated by Grant and Al-Najiar (1976). Alkyl Carbazoles in Norman Wells Crude Oil
can be degraded by microorgranisms (Phillip et al., 1984).
In order to industrialize biodegradation processes for desulfurization and
denitrogenation, it needs to maximize the rate of sulfur/nitrogen removal and extend the
biocatalyst life, thereby substantially reducing capital and operating costs. Cell
immobilization is an effective way to realize it. For example, Pseudomonas delafieldii
was immobilized in magnetic polyvinyl alcohol (PVA) beads using hydrophilic
magnetic nanoparticles (Shan et al., 2003). Their desulfurizing activity increased slightly
from 8.7 to 9 mmol sulfur/h-kg of dry cell. Moreover, the magnetic immobilized cells
could be easily collected or separated magnetically from the biodesulfurization reactor.
Besides, the combination of nanomaterials and cells is also applied in the
biodesulfurization process. Cell-nanomaterials complex is generated by assembling or
adsorbing nanoparticles on the surfaces of microbial cells, which increases the reaction
activity of original cells, and is helpful to lessen environmental pollutions. For example,
magnetite nanoparticles were assembled on the surfaces of P. delafieldii cells and the
cell-nanomaterials had distinct super paramagnetic properties, which could conveniently
be collected by application of an external magnet or operated in a magnetically
stabilized-bed reactor (Shan et al., 2005a). A magnetically stabilized fluidized bed is a
highly efficient bio-reactor that takes advantage of both fluidized beds and fixed beds,
and has been applied in treatment of wastewater or solid waste. The biodegradation rate
of polycyclic aromatic sulfur compounds increased over 2 folds by self-assembling
nano--alumina on cell surfaces (Shan et al., 2005b).
14.2.4 Roles of Nanomaterials in Agriculture and Food Systems
Nanomaterials have the potential to revolutionize the agricultural and food
industry with new tools for disease treatments, rapid disease detection, etc. With their
special characteristics at the nanoscale, nanomaterials could offer a tremendous
 
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