Environmental Engineering Reference
In-Depth Information
and rock between the surface water sources and the deep aquifer filter out
the larger pathogens.Then all you need to worry about is viruses and bac-
teria. And then this unit can handle it well.
Finally, UV transmittance in water is hindered by high turbidity and cer-
tain dissolved salts. However, we estimate that most waters are adequately
transparent to UV-C to enable this technology to disinfect the water. We
know that we can disinfect water up to 20 Nephalometric Turbidity Units
of turbidity. Raw water with this turbidity is 20 times more turbid than
what the US EPA and the WHO recommend for drinking water. So, if the
raw water has higher turbidity, one must filter it to reduce the turbidity
anyway.
Those who travel to developing countries are familiar with the condi-
tions in which much of the world lives. In any given village, the creek run-
ning through the slum collects all the wastewater. This is the stream along
which children play, and this is also the water for these people to wash their
clothes. In a community, for example a typical village in Orissa (a poor state
in India), one UVWaterworks unit would save about one diarrheal death
per year in a community of 1,000 people. Presently, there are about three
diarrheal deaths per year of children below age 5 in a typical village of
1,000 in Orissa. We can save (and take credit for) only one; the other two
deaths will have to be avoided through public hygiene, public education,
and adequate treatment of human and animal waste. If all of that is done,
you would avoid all three deaths. So, over the 15 year estimated life of a
UVWaterworks unit, it would certainly avoid 15 deaths by our estimate. It
would also avoid the stunting of 150 children growing up in this commu-
nity over these 15 years. UVWaterworks uses 6,000 times less energy than
is needed for disinfection by boiling the same amount of water over bio-
mass cook stoves. Including grid electricity, consumables, and amortization
of capital, the annual cost of disinfection is less than 14 cents per person.
The units have undergone limited field trials in India and in South
Africa. In Manila, a flourishing business has been established by the distrib-
utor of these devices. The distributor sets up water vending kiosks built
around pumps, filters, stainless steel water storage tanks, and one unit of
UVWaterworks.As feedstock, he uses the available city water supply (which
is of uncertain quality), or he obtains water from wells.The raw water is fil-
tered, disinfected with UVWaterworks, and sold at very low cost to people
from low-income or slum communities. But he recovers his investment
