Environmental Engineering Reference
In-Depth Information
the arid Middle Eastern Desert, or the Gobi deserts; however, this technology could well
have been born more than 2000 years ago. Harnessing fog from PAFCs has been histori-
cally one of the most ancient methods utilized by humanity and societies in arid areas. It
is a technique that has been improved over the ages and developed by many researchers
and cited throughout the years, all of whom have experimented with various types of
screens and architectures, and have achieved varying results [8]. It has been a success as a
low-tech solution by combining some form of mesh material strung tightly on poles, and
supported by gutters to collect droplets that are fed into pipes and stored in tanks, and
can be readily thought of as a fog fence. Today, it continues to be largely unknown by the
general populace.
Parallel early developments in the Middle East and in South America occurred roughly
simultaneously. South American legend has it that the pre-Columbian-culture people from
the area of what is now known as Chile, Peru, and Bolivia, who tended to their llama herds,
were among the earliest pioneers [8]. These people essentially discovered a way to use the
blankets made from the wool from their very own locks by placing these in an upright
and perpendicular position facing the wind direction. Probably while seeking shelter, they
found that the mist through their garments would soak them completely. It was not long
before they found that the water condensed upon their blankets could be used to capture
dew, and when the droplets reached a suficient size, these would trickle down to the
ground. To harness this water, they would simply place a channel and a receiver beneath
them. They were thus able to store enough water to meet their own and their lock's needs,
in the
altiplano
(high plains) regions, in two of the driest deserts on the planet where pre-
cipitation seldom, if ever, occurs. The name, in Spanish, for this technique of capturing
water from mist is the aboriginal word
camanchaca
, a word that is also used for a very
common type of fog on the Paciic coasts of South America today. The fog banks come in
regularly from the Paciic Ocean breezes from the Humboldt Current and climb up the
pre-Andean foothills and slopes, traveling many miles into the South American continent.
Similarly and roughly about the same time in the Middle East, air wells from caves
were well known to have been tapped for harvesting of water. In the Middle Ages, dew-
ponds in Europe were also used to collect water, especially in times of plagues or droughts
(Figure 29.2).
29.3 Background and Technical Developments
Nature itself has provided us with its own multistructured and multifunctional inte-
grated fog collection systems, as seen in a variety of plants such as the cactus which
depend entirely on its own capability for fog collection. The gradient of the Laplace pres-
sure, surface energy, and multifunction integration assist the cactus with fog collection
[9-13]. Another case in point from nature is that of the Namib beetle (
Stenocara gracilipes
),
which is capable of leveraging and enhancing its ability to catch water. When a moist sea
breeze makes contact with the hydrophobic region of its shell, a small chemical imbal-
ance occurs, which leads to the formation of droplets that, upon reaching suficient size,
are sent through the guttulae that extend to the mouth of the insect where they are later
absorbed.
These irst successful and humble attempts in capturing water from dew caught the
attention of several researchers, including Boussingault in 1844, who is credited with
