Environmental Engineering Reference
In-Depth Information
against large volumes, overall equipment design, eficient data previously available, and
clear optimization.
AWC continues to be improved by way of equipment designs becoming more eficient
from the point of view of industrial and materials engineering. The irst steps in apply-
ing nanotechnology advancements in AWC began 2 years ago. At present, they are being
tested in various applications in Spanish laboratories to ensure the holding of a propri-
etary primer (serving as a bridge between the base weave and active ingredients) and to
ensure that no sloughing or possible toxicity issues arise from their use. However, these
steps are merely intermediary, with the inal results being sought for these meshes, and
the integration of nanoparticles in the raw base material of the substrates used for each
type of systems is done to optimize time and costs of manufacturing.
It is also a known phenomenon that water droplets are absorbed within the mesh as
in the case of most hydrophilic applications, whereas on hydrophobic surfaces droplets
are formed bigger in size and roll through without being absorbed. Pollock reported that
there is some evidence to show that incoming water slides over a very thin layer of greater-
density water, the thickness of which is on the nanoscale. Pollock has also reported that
the hydrophobic interaction extends tens of nanometers. Superhydrophobic forces can pro-
vide extra supporting force for loating objects immersed under water. A superhydropho-
bic surface can provide 0.4 mN force/cm
2
, more than a lat surface can [37]. The vertical
component of a superhydrophobic surface is increased as the air passage in the center
of the surface provides extra buoyancy force. What happens at the water hydrophobic
interface is not conclusively known. It is believed that water lows through small pores in
hydrophobic membranes. A tiny cushion of low-density water between the hydrophobic
surface and bulk water seems to exist. A dynamic interface is formed where water touches
and leaves the surface repeatedly [38]. As suggested, a dynamic mechanism of droplet for-
mation at an atomic level has not yet been fully conceived by atomic force microscopy and
refractometry analysis. This would help the generation of new designs of mesh surfaces.
Metallic meshes produce greater output than a polypropylene mesh, and seem to be a
better choice when considering the longevity of a PAFC's useful lifetime. There is no evi-
dence to suggest that aluminum or corrugated iron, as was used in Oman, would be better
than nets of polypropylene in terms of yield. Metals and nylons are both being studied and
contrasted concerning their use as collection devices [39].
In recent work by the author (Ahmad), nanostructured hydrophobic surfaces were cre-
ated in an attempt to mimic the Namib beetle's back for microcondensation of fog drop-
lets. Stainless mesh panels were cleaned with HCl and acetone followed by washing with
distilled water and drying. They were subjected to ultra shot peening at 20 kHz, the shot
diameter being 1 mm. They were annealed at 350°C and cooled in air. The grain size
was decreased to 25 nm. An emulsion of 20% polytetraluoroethylene, 10% polyvinyl alco-
hol, and 10% sodium dodecylbenzene sulfonate in deionized water was produced. It was
homogenized in an ultrasonicator at a speed of 3000 rpm. The emulsion was sprayed on
a mesh panel with compressed air. The panels were subjected to laser etching immersed
in an ethanol solution of luoro-alkylsilane for 4 h. A solution of polyacrylic-acid-water-
propanol was applied on the panels. The panels were transferred to an oven and dried,
followed by rinsing and cleaning. The WCA was measured and was ensured to be not less
than 150°. The panels were ixed on frames and tied to galvanized iron posts by cables.
Drainage was through a galvanized iron pipe (15 cm). It was covered with meshed covers
to prevent contamination. The reservoir was made of clay and straws (using a torrefac-
tion process), resting in a inal layer of concrete to keep the water cool.
Aloe asperifolia
was
planted in the vicinity of a fog trap or PAFC. The system was connected to a data logger to
