Environmental Engineering Reference
In-Depth Information
This chapter describes the various technologies involved in AWC and focuses on the pursuit
of a specialized mesh with a suitable outer layer structure that has been furnished with tech-
niques and coatings containing both superhydrophilic and superhydrophobic capabilities, in
order to achieve approximate optimization of AWC as close as possible to 100% eficient. The
recent advances in nanotechnology have shown the way to create a hierarchical superhydro-
phobic nanostructured surface achieving water contact angles (WCA) >90° (a standardized
method of determining the degree of hydrophobicity). These techniques hold great promise
for areas where water is scarce, and can be furnished readily, including in those areas with
a high water demand and even in those that are limited by the scarcity of clouds, or in areas
where relatively low fog density preclude their use. This optimization increases the current
footprint of areas that can now be made to capture atmospheric water, not only to be suit-
able for irrigation or cattle grazing but also for actually sustaining entire communities even in
urban areas close to coastal regions and deserts.
By utilizing both superhydrophilic and superhydrophobic surfaces on the capturing
substrates, a renewed interest in providing for areas of water scarcity has been achieved.
Water from fog is currently harnessed at heights of at least 400 m above sea level. Below
this altitude, traces of salt may still be present in the captured water.
AWC has gone beyond our own planet, as new AWC viability projects are currently
being conducted by the National Aeronautics and Space Administration, including
planned AWC systems such as that in the planned Mars Base Station, which intend to rely
on zeolites for water capture [1].
Several types of commercial AWC systems exist today, and we differentiate between
the two main ones: active and passive systems. Active systems, including state-of-the-art
atmospheric water generator (AWG), are essentially dehumidiiers requiring some form of
electrical power to drive a compressor used to extract moisture from the air and convert
it to pure water. These are compact and can be extremely eficient. The need for electricity
from the utilities networks has been mitigated by the application of eficient solar cells or
wind turbines, allowing these facilities to function just about anywhere. The costs ulti-
mately depend on the price of electricity needed to run them, including infrastructure
maintenance and repair of such active systems requiring storage of energy such as bat-
teries, which themselves are being rapidly improved by nanomaterials such as graphene.
On the other hand, passive atmospheric fog collector (PAFC) technology relies instead
on wind power from well-known and established ocean weather patterns to harness water
from the atmosphere without the use of additional power sources. These units began as
specialized forms of fog fences and are used in coastal areas where inland winds bring
fog, at high altitude areas from 400 to 1200 m, since below these altitudes traces of salt may
render the captured water unusable.
Ultimately, these are meant to be solutions as low-cost units for water-scarce nations but
are eficient enough to sustain reliable sources of water even on highly populated or devel-
oped megacities such as Lima, Peru. According to a 1995 study by the Ottawa International
Development Research Center, the following countries are excellent sites for the implementa-
tion of this technology: Nepal, Eritrea, Yemen, Oman, and Kenya, including the entire Atlantic
coast of Africa: Angola, Senegal, Congo and DR Congo, Namibia, South Africa, and Cape
Verde; the entire east coast of the South Paciic, including Mexico, Chile, Bolivia, Peru, Ecuador,
and Colombia; and in Asia: China, Pakistan, Mongolia, India, Bangladesh, and Sri Lanka. Gulf
countries such as Oman, Saudi Arabia, and Yemen can readily afford this technology, and are
eager to ind economic and reliable alternatives to desalinization plants.
PAFCs can be small units for a single residence 2-5 m
2
, or can be very large arrays with
hundreds of square meters of surface area suitable for entire communities. For example, a
