Environmental Engineering Reference
In-Depth Information
technology. Furthermore, embedding the clay particles in a polymer can slow down the
adsorption process because the adsorption active sites are concealed or enveloped by the
polymer. This can be dominant in composites prepared by the melt-blending method,
which use hydrophobic polymers. Consequently, there are long equilibration periods in
adsorption experiments using composites, compared with when the iller is used inde-
pendently. One of the most reported drawbacks in composites is weight increase. Weight
increase tends to favor the settling of the composites in water; hence, vigorous mechani-
cal stirring would be required. Finally, depending on the polymer used in preparing the
composite, erosion of support in desorption studies can be a serious problem. Desorption
of the adsorbate from an adsorbent usually occurs under harsh conditions.
The development of nanotechnology-enhanced membranes comes with challenges such
as dificulty in dispersion of nanocomponents and cost related to large-scale application.
Hashim et al.
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recently reviewed the various remediation technologies for heavy-metal-
contaminated groundwater. It was observed that high-pressure membrane and iltra-
tion technologies, while they have a high removal eficiency of heavy metals, their major
drawback is clogging, which subsequently requires regeneration of the ilter materials.
However, the regeneration of the materials is not as frequent as is the case with activated
carbon.
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Thus, whether the metal removal mechanism is by iltration or adsorption, it is
necessary to backwash or desorb the metal residues from the surface of the membranes.
This is a challenge that cannot be avoided completely but can be made minimal. Other
technical challenges may include the complexity and expense of the concentrate (residu-
als) disposal from high-pressure membranes. This often translates to high maintenance
costs of the membranes.
20.5.1 Opportunities
Composites prepared by the melt-blending method can be molded into strips of different
sizes and shapes. This makes it relatively easy to recover the composites after heavy-metal
capture in water. This is crucial because to obtain clean water, the spent adsorbent should
be successfully removed from the water. The size of the strip affords better handling and
cleaning of the composites, compared with powder adsorbents like activated carbon and
clay. Additionally, embedding the adsorbents like clay in a polymer reduces the risk of
sludge formation.
On the other hand, the ability to modify the surface and structure of membranes using
various chemical strategies provides opportunities for the development of nanomem-
branes. Other materials such as graphene sheets are now being exploited for the removal
of heavy metals.
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Membranes generally consume less energy and are suitable for large-
scale use and can easily be integrated to existing plants.
20.6 Conclusions
Nanotechnology is making use of materials measuring 100 nm or less that have proven
to display unique properties and characteristics that may offer solutions to water quality
problems currently facing our planet. The ability of these nanomaterials and nanoparticles
to alter chemical and physical properties of substances can be exploited in the processes
leading to improving the quality of water signiicantly. In this chapter, various examples
