Environmental Engineering Reference
In-Depth Information
Picture 9.2
Industrial cooling towers.
Courtesy of Argonne National Lab, US Department of Energy.
Condensates from process or from refrigeration equipment are low in minerals, so when-
ever possible they are both good sources of water for boilers and other applications than water
with low solid content.
Rainwater harvesting
As reserves of freshwater decline rainwater harvesting is an option worth considering. It is not
only an inexpensive source of water but also solves the problem of storm water runoff. The
main obstacle of rainwater harvesting is the need for large reservoirs for storage.
Rainwater can be collected from any horizontal or semihorizontal surface. Therefore, building
roofs make ideal catching surfaces, mainly in industrial or commercial buildings that have exten-
sive roof areas. Parking lots are able to capture large volumes of water, too, but they are normally
contaminated with oil, fuel, dust, and polycyclic aromatic hydrocarbons from seal coats.
One millimeter of rainfall is equivalent to 1 liter of water per square meter of horizontal
surface. So, for instance a region that has an average annual rainfall of 1500 mm (59 inches)
the potential for water capture is 1500 liters/m
2
each year.
Most buildings already have rainwater collection systems in place with downspouts that
take rainwater away from the building. These installations can be retrofitted for water harvest-
ing by diverting the water stream to tanks or a pond. Because most of industrial roofs are flat,
it is a good practice to install siphonic roof drains that expedite water drainage and the convey-
ance of water in horizontal pipe sections. Water quality can be significantly improved with the
installation of roof-wash systems, which redirects water away from the holding tank during
the first few minutes into the storm thereby letting the accumulated dirt wash away.
Rainwater can be used for any nonpotable use, such as in cooling towers, landscape irriga-
tion, fire suppression, and toilet flushing. In areas with low concentrations of environmental
air pollutants, rainwater can be treated by filtration followed by chlorination and used for
potable applications. The application of membrane technologies is another technique that can
be used as a disinfection technique.
