Environmental Engineering Reference
In-Depth Information
light used in the Puralytics process broaden the effectiveness of this process. Photolysis
is the direct absorption by a contaminant molecule of photons with suficient energy to
directly dissociate chemical bonds. Shorter wavelengths are more energetic and there-
fore more effective over a wider range of chemical bonds. Hundreds of organic contami-
nants have been shown to photodegrade under UVA, UVB, and UVC light through direct
photolysis.
24.6.5 Photodisinfection
The primary mechanism for sterilization of organisms is disruption of DNA molecules,
thereby preventing reproduction. With multiple wavelengths, very high light intensity,
and the other synergistic processes, pathogens are disinfected more effectively than
standard germicidal irradiation. The combination provides improved sterilization of
aggressive viruses, resistant bacteria, protozoa, and molds. UV germicidal irradiation
with mercury lamps is a well-established process for sterilizing pathogens. For germi-
cidal applications, the 250-280 nm wavelength band is effective at disrupting the DNA of
microorganisms. Monochromatic radiation within this band, such as the 254 nm radia-
tion from a low-pressure mercury lamp, sterilizes microorganisms; however, a band of
wavelengths above 265 nm would be even more effective [14] and reduce dark repair of
DNA [15]. Higher-pressure mercury and xenon lamps produce broadband radiation—
ineficient for disinfection or for activating a semiconductor photocatalyst. Moreover, UV
lamp sources are fragile, and mercury lamps in particular are environmental hazards.
UV LEDs, spanning multiple wavelength bands, are effective, safe, and can uniformly
illuminate a large area.
These ive photochemical processes destroy a broad range of contaminants, effectively
removing them from the environment, in a self-cleaning process. Since the nanomaterials
are not consumed by these reactions, and only metals remain on the catalyst over time,
the media does not need to be replaced until the catalyst is saturated with metals. These
reactions can be enabled either through direct sunlight illumination or by using solid-state
LEDs to provide the precise wavelengths of light that are needed. The combined reactions
primarily produce pure H
2
O, dissolved CO
2
, and trace minerals as by-products.
These photochemical processes, working together within the Puralytics products, pro-
vide a disruptive new entry to the water puriication market and enable new applications
not currently possible.
24.7 Product Implementation
Puralytics has developed this technology into two scalable product platforms, the Shield
and the SolarBag.
24.7.1 Shield
The Shield addresses industrial and commercial water treatment applications with an
electrically powered, LED-activated, stand-alone puriication system or system compo-
nent. This unit has a small footprint and can be used in series or parallel for higher water
lows or contaminant removal rates, typically for applications <20,000 gallons per day.
