Fog Harvesting-A A +A
By Rox Peña
Thursday, September 12, 2013
IN TODAY'S worsening water crisis, many innovative ways of getting clean, potable water are being resorted to. Water, which used to be very abundant, is becoming scarce due to multiple demands for domestic, industrial and agricultural uses. What's more, pollution has contaminated water bodies which are traditional sources of clean water. Over extraction of groundwater on the other hand is causing the seepage of salt water in coastal areas.
With the depletion of traditional sources, rich nations turn to technology.
In the Middle East, potable water is obtained by desalination. In Singapore, treated wastewater is further processed and turned into potable water. The product is called NEWATER.
An inexpensive way to get water is by rainwater harvesting. This is already a common practice. In fact, I’ve seen the rainwater harvesting facilities of at least two companies inside Clark Freeport Zone. At Hansa Toys, rain falling on their roof is collected and stored in a large tank. At the Singapore Airlines aircraft repair facility inside CIAC, they have a well-planned rainwater harvesting system which is integrated into the building design.
There’s a system of collecting water which is not yet done in the Philippines - fog harvesting. Did you know that fog or dew harvesting is an ancient practice? Archaeologists have found evidence in Israel of low circular walls that were built around plants and vines to collect moisture from condensation. In South America’s Atacama Desert and in Egypt, piles of stones were arranged so that condensation could trickle down the inside walls where it was collected and then stored.
Fog is collected by constructing fog-catchers that look like tall volleyball nets slung between two poles. They are made of a polypropylene or polyethylene mesh that is especially efficient at capturing water droplets. When the fog rolls in, the tiny droplets of water cling to the mesh, and as more and more cluster together, they drip into a gutter below that channels the water to a water tank. Fog collectors are best suited to high-elevation arid and rural areas like Baguio City.
Let’s learn the basics of fog harvesting from http://www.fogquest.org/.
What is fog? Fog is the same as a cloud except that it touches the ground, whereas a cloud has a base that is above the ground. When a cloud is moved by the wind and flows over and around a mountain, fog is present wherever the cloud touches the terrain. What is important in the fog collection process is that fog is composed of tiny liquid water droplets from 1 to 40 micrometers in diameter. A typical droplet diameter is 10mm.
There is typically from 0.05 to 0.5 grams of liquid water in a cubic meter of fog. One large fog collector, with a 40 m2 collecting surface, will typically produce an average of 200 L per day throughout the year. On some days no water is produced. On other days as much as 1000 L will be generated. The variability depends on the site. Choosing an appropriate site is of utmost importance. There are both day-to-day variations in fog-water production as well as seasonal variations, as is the case with rainfall.
Is fog water clean? Fog water chemistry has been studied and found to meet World Health Organization drinking water standards. Because it is produced in remote areas, few sources of potential contamination are present.
Normally bacterial contamination would also not be an issue since it is very unlikely that there would be harmful bacteria in the fog. The mesh itself rapidly cleans itself from any dust that may have settled on it during a dry period. Once the water is produced by the fog collector the same precautions and considerations apply as for any other water source.
Published in the Sun.Star Pampanga newspaper on September 13, 2013.