Page 127 - Materials Chemistry, Second Edition

108 Life Cycle Assessment of Wastewater Treatment

Removal rates of 65%–98.3% were obtained for the range considered. The effi-
ciency of Reactive Blue 19 removal was found to increase as the catalyst dosage
−1
−1
was increased up to 300 mg L . At 500 mg L , the removal of dye decreased
by 30%. Similar results were observed in previous studies, where beyond a cer-
tain dosage of Fe O nanoparticles, the degradation efficiency dropped, which
4
3
was likely caused by high nanoparticle concentrations. Peroxidase-like activity
occurred on the surface of the Fe O nanoparticles due to the presence of iron ions.
4
3
An excessive dosage of nanoparticles could lead to the formation of aggregates that
would reduce the available surface area and thus the density of surface-adsorbed
H O (Huang et al., 2012). The results obtained in this work point to the heteroge-
2
2
neous Fenton process as a promising technology for the treatment of textile waste-
waters. However, further studies are needed to achieve a complete characterization
and understanding of the process. As well as other variables, the evaluation of the
reaction rates and the role of iron nanoparticles have to be addressed in the devel-
opment of this technology.
6.3.3 nanobiocaTalysTs baseD on silica-coaTeD, oleic
aciD–coaTeD, anD polyeTHyleniMine-coaTeD MagneTic
nanoparTicles anD THeir use in Dye DecolorizaTion
Oxidoreductases, such as laccases, have been used in oxidation processes such as dye
decolorization because of their high activity, selectivity, and specificity (Wesenberg
et al., 2003). Stability and recovery of the biocatalyst are the main concerns when
using enzyme biocatalysts in industrial applications (Cabana et al., 2011). However,
these drawbacks can be overcome through the immobilization of enzymes, which
can lead to improvement of the stability, separability, and reusability of biocatalysts
in continuous operations (Duran et al., 2002). Different supports providing a range of
functionality, morphology, and physical properties have been studied for the immo-
bilization of enzymes (Lloret et al., 2011; López-Gallego et al., 2005; Kunamneni
et al., 2008). Recently, nanostructured materials have attracted considerable interest
as supports (Zhao et al., 2011).
Magnetic nanoparticles (mNPs) are characterized by a magnetic core that can
ensure their easy recovery with a simple magnet. In addition, mNPs provide a high
superficial area for the binding of enzymes, low mass transfer resistance, less foul-
ing, and a decrease in operational costs, which make them potential candidates for
enzyme immobilization (Kalkan et al., 2011). The mNPs should be coated with
organic molecules (surfactants, biomolecules, or polymers, among others) or inor-
ganic layers (silica, metal oxide, etc.) to provide a proper surface and retain the sta-
bility of magnetic iron oxide nanoparticles (Wu et al., 2008).
In the present work, laccase immobilization by covalent bonding onto mNPs
coated with silica, polyethylenimine (PEI), and oleic acid was developed, and the
immobilized enzyme was applied for the decolorization of two different dyes:
®
Methyl Green and Reactive Blue 19. Furthermore, a Microtox test based on the
luminescent marine bacterium Vibrium fischeri was performed to investigate the