Environmental Engineering Reference
In-Depth Information
Our device does not appear to have been difficult to design; it is just that
no one seems to have tried to design it before. Something like this could
have been done 10 years ago by someone else with far less technical knowl-
edge and support than our team had. It did not require a national labora-
tory and all the high-tech machinery we ended up bringing to bear on the
problem.
The use of a low-pressure mercury plasma, as in kitchen fluorescent
lamps, is a mature technology; it has been in use for half a century. Some
95 percent of the radiation from that plasma actually comes out as “UV-C,”
at a wavelength to which DNA is extremely susceptible. There is no light
of that wavelength available in the solar spectrum on the Earth's surface.
The ozone layer absorbs it all. Maybe that is how the DNA on the planet
evolved to remain susceptible to it, since it can receive no damaging UV-C
from sunlight. It turns out that a standard fluorescent lamp produces lots of
UV-C light of this wavelength. But the inside of the tube is coated with a
fluorescent powder, which absorbs the UV-C and emits visible light. If you
do not have that powder and if your tube is made out of quartz rather than
glass, so all the UV will come out, then you already have a mature tech-
nology that the factory perfected in some sense, mass produced, robust, like
your kitchen fluorescent lights again. And any DNA that is exposed to this
UV light gets damaged severely; adjacent base pairs in the DNA double
helix get covalently bonded.You can think of them as fused together. It's
like having a zipper jammed so that when the bacterium of the virus tries
to unzip the DNA for replication, the two adjacent base pairs are fused
together, and the DNA cannot be replicated, so the bacterium or the virus
is unable to reproduce. If the UV dose to the DNA is high enough, you
will fuse a huge number of adjacent base pairs in this DNA, essentially mak-
ing that DNA useless for the organism, and the organism dies. It cannot
infect, it cannot replicate.
We designed and built the unit, we went through the first level of field
testing in India, and based on the feedback from the field we redesigned the
unit. The final design is compact, simple, lightweight, and delivers more
than 120 milliwatt-seconds of UV-C energy per square centimeter of water
surface, in 12 seconds. We tested the unit's performance in reducing the
concentration of
E. coli
introduced in the inlet water.
E. coli
is the standard
test organism used by World Health Organization and the US Environ-
mental Protection Agency to test the effectiveness of various disinfecting
methods against waterborne pathogens.We found that our apparatus, which
