Environmental Engineering Reference
In-Depth Information
membrane-based systems or use of revolutionary new material such as carbon nanotubes
or fullerenes, so that they can be easily integrated with alternative renewable sources of
power such as solar energy or wind energy.
For disinfecting the water, chlorine is used primarily because it can be implemented
relatively easily without the need for power as in the case of disinfection utilizing UV
radiation, although UV disinfection is the preferred method as it does not involve addi-
tion of any chemical or adverse side effects of forming by-products that may be harmful to
the health. Nanotechnology has the potential to create passive disinfection systems such
as use of nanoscale silver particles deposited on a high surface area matrix that does not
require any power or use of active photocatalytic material deposited on a high surface area
substrate that can provide lasting disinfection effect using natural light.
Water-quality tests such as those for pathogens take several hours or days to get results
back as the water sample has to be collected and microorganisms allowed to grow and
multiply, before they can be detected and counted. If there is a problem with the water
treatment system, there is no real-time feedback to the plant operator. By the time water
test reports are back, users have already consumed the water. The response to the problem
is not immediate, which can put the consumers at risk. Drinking water regulations require
that bacterial counts for species such as
Escherichia coli
be undetectable in 100 mL of water.
Other nonspeciic bacteria counts need to be less than 100 or 1000 colony-forming units
(CFU) per mL. The challenge here is that for real-time measurement, in-line tests have
to be sensitive enough to detect trace amounts of bacteria and be rapid enough to detect
them in a short interval of time. Here nanotechnology can be of immediate help in taking
several microsamples and provide the capability of detecting bacterial proteins in a very
short time.
Similarly, contaminants such as arsenic and mercury are very toxic in nature and health
agencies have determined that prolonged ingestion of arsenic in drinking water contain-
ing >10 ppb can lead to cancer. Regulatory agencies are considering further lowering the
maximum allowable limit to <5 ppb. The challenge here is that there is no cost-effective
technique available that can consistently detect arsenic levels to 5 or 10 ppb, while at the
same time be in-line and compatible with a remote monitoring system. Equipment employ-
ing adsorption or emission spectroscopy are very expensive, costing several hundred
thousand dollars and are uneconomical to implement at a small community level whereas
less expensive arsenic test strips that rely on conversion of arsenic in water samples to
arsine gas and comparison of strip color to color standards are subjective and untenable
as an in-line method compatible with remote monitoring. Here again, nanotechnology
can provide the beneit of developing small, affordable sensors that will have the ability to
rapidly detect trace levels of the contaminants, while integration into suitable electronics
can render it compatible with remote monitoring.
To summarize, there is a need for robust cost-effective technologies for water treatment
and contaminant analysis that can withstand the harsh ield conditions while enabling
automated operation and real-time remote monitoring
.
