Environmental Engineering Reference
In-Depth Information
About 2 billion people do not have tap water supplied to their home.
About 4 million children, mostly under the age of 5, die each year from
drinking biologically contaminated water (that is, water contaminated with
human and animal wastes containing various pathogens). A single person
sick with a diarrheal disease may have initially ingested a few hundred
pathogens; however, with each diarrheal stool he or she passes, 10 billion
pathogens enter the environment.That is an enormous multiplier. If waste
is not treated adequately, the pathogens get in the water supply and we have
an outbreak. Then there is the problem of stunted children. Children who
do survive diarrheal diseases have reduced absorption of nutrients in their
system for periods that are up to four times longer than the actual diarrheal
episode itself. That results in a child whose growth is stunted. In addition,
billions of work hours are lost to diarrheal diseases each year.
In downtown Mumbai (Bombay), there are slum areas right next to
high-rise apartments. One often sees women who live in the slums fetch-
ing water from a collective tap. These women probably work nearby as
housemaids; many of the men living in the slums work as office boys or in
factories.
The common methods of treating drinking water are chlorination and
boiling. Chlorination requires maintaining a supply chain of necessary
chemicals and a trained operator. Water overdosed with chlorine becomes
unpalatable. Boiling, of course, requires a huge amount of biomass, or a lot
of kerosene fuel, which is very expensive. A family of five requires at least
10 liters, or 10 kilograms, of drinking water per day. To boil 10 liters
of water requires about 3 kilograms of fuel wood per day, and that is
beyond their means.Three kilograms is more than their current daily con-
sumption of fuel wood just for cooking food, so doubling that amount
is not something that people can manage or that the environment can
sustain.
What we were looking for in the summer of 1993 was something that
would be energy efficient and low in cost, would treat unpressurized water,
and would be able to disinfect water that people carry in pots and buckets
and cans.We wanted rapid throughput. People do not want to invest much
more time than they already do for collecting water. For good field per-
formance, we wanted a device with low maintenance and high reliability,
and we wanted it to be based on mature components—preferably off-the-
shelf components, so we would not have to worry about technical failures
or immature manufacturing processes.
