Environmental Engineering Reference
In-Depth Information
(2004) reported a sensitive and rapid method for detection of
E. Coli
O157:H7 using
QDs. Recently, liposomal nanocapsules were used as delivery vehicles of nutrients,
nutraceuticals, food additives, and food antimicrobials that could aid in the protection of
food products against growth of spoilage and pathogenic microbes (Taylor et al., 2005).
14.3.1 Converting Wastes into Valuable Products
Most industrial and agricultural processes yield low value solids or waste
streams. These wastes often contain potentially valuable components, such as proteins or
carbohydrates, but the processes for efficient recovery of these products are lacking.
Bioconversion [e.g., by the application of microorganisms or enzymes (biocatalysts)]
has attracted increasing attention as a possible means to decrease the environmental
burden of industrial waste streams and, moreover, to convert these wastes to potentially
valuable products. For example, bioplastics and biopolymers can be produced from plant
wastes by microorganisms. Apparently, enzymes are the core of the bioconversion
process for industrial and agricultural wastes (Koeller and Wong, 2001).
Immobilization, the process of fixing an enzyme into the specific spaces of an
inert support, may help to solve some of the problems of enzymes as industrial
biocatalysts, such as enzyme recovery, enzyme stability, enzyme selectivity, reduction
of inhibition by the medium or products. Moreover, the use of an immobilized enzyme
permits to greatly simplify the design of the reactor and the control of the reaction
(Chibata et al., 1986; Katchalski-Katzir, 1993; Mateo et al., 2007). As a result,
economically sound and environmental friendly production of high-value products by
using industrial and agricultural wastes as substrates is feasible.
The support for the enzyme plays an important role in the overall yield of the
bioconversion process (Krajewaska, 2004). Nanomaterials, due to their specific
properties, such as small size, superparamagnetic, electric, and optical properties, are
one of the best candidates for enzyme immobilization. For example, silica with nano-
sized pores was used for immobilization of Glutaryl-7-ACA acylase (Kim et al., 2004).
Due to its excellent conductivity, a large surface area and the good biocompatibility ring
of gold nanoparticles, a gold nanoparticles-mesoporous silica composite has been
developed as a novel enzyme immobilization matrix (Bai et al., 2007). Using the layer-
by-layer technique, poly(amido amide) (PAMAM) dendrimers with cobalt
hexacyanoferrates-modified gold nanoparticles were alternated with poly (vinylsulfonic
acid) layers on ITO (indium tin oxide) electrodes. This film was used as a substrate for
immobilization of glucose oxidase in the presence of bovine serum albumin (Crespilho
et al., 2006). Porous hollow silica nanotubes were employed as a support for
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