Environmental Engineering Reference
In-Depth Information
we named, UVWaterworks, reduces
E. coli
concentrations by a little more
than a factor of a million, and it reduces virus concentrations by a little
more than 10,000.
The viruses against which we tested this were polio virus and rotavirus,
the most common pathogenic waterborne viruses.The rotavirus gives diar-
rheal dysentery and is the most resistant to UV disinfection among all
diarrheal pathogens. We also tested the technology against waterborne
concentrations of real pathogens clinically isolated from hospital patients in
Bombay, including cholera, shigella, and typhoid pathogens, and found the
technology to be very effective.
With UVWaterworks, 5 cents' worth of grid electricity—about half a
kilowatt-hour—suffices to disinfect a day's drinking water for 1,000-2,000
people. So it seemed pretty cheap. It is also extremely simple, embarrass-
ingly simple. As I said earlier, nobody appears to have bothered to do it
before us, but it was there for anyone to build. And the reason I think
nobody bothered to do it is because, on the one hand, these people's lives
are cheap.You cannot make too much money off somebody who dies of
cholera in Bangladesh. These people do not have votes, they do not have
the technical know-how to do it themselves.
Inside the UVWaterworks, you have an aluminum reflector. Below it is
a UV lamp suspended in air above the water's surface. All parts that contact
the water are made with stainless steel so there is no corrosion to worry
about. Below the UV lamp, water flows in an open channel under gravity
in the stainless pan and comes out at the other end of the device. That is
essentially what is inside the device.
By the way, disinfecting with UV-C light is not a new idea. It has been
known for almost a century. However, all other water disinfection devices
using UV light require the UV lamp to be encased inside a quartz tube,
and the whole thing placed coaxially inside a stainless steel cylinder and
immersed in axially flowing water.This design requires pressurized water to
drive the flow through this narrow gap between the quartz tube and the
stainless chamber, which means that the 2 billion people who fetch water
in buckets cannot use it. So, it is extremely surprising and slightly irritating
that a simple device such as this has not been developed for all these
years.
The second innovation was, of course, ensuring correct hydrodynamics
for the flow in this pan. We wanted to ensure that all the water moves
almost as a block rather than various parts of the water moving at different
