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UV light disinfects wastewater effectively
A
Hanovia product story
Edited by the Manufacturingtalk editorial team
Nov 27, 2003
Ultraviolet light is highly effective against pathogens resistant to traditional disinfection techniques and, by reducing chlorine doses, it leads to lower concentrations of by-products.
Ultraviolet light (UV) is widely used for disinfecting water and wastewater.
It is highly effective against pathogens resistant to traditional disinfection techniques and, by reducing necessary chlorine doses, it leads to lower concentrations of unwanted disinfection by-products.
There are currently two main UV technologies: low-pressure and medium-pressure (LPUV and MPUV respectively).
The former emits UV light at a single wavelength of 254nm, while MPUV lamps emit UV over a wide spectrum between 185 - 400nm.
UV from both types of lamp kills microorganisms by destroying their DNA.
A major advantage of MPUV is that it not only destroys microbial DNA, but also important DNA-repair enzymes, something LPUV lamps do not do.
One concern recently raised about the use of MPUV for water treatment is whether low levels of nitrite (NO2-) formed from nitrate (NO3-) as part of the disinfection process, pose a health threat.
While nitrite formation is negligible with LPUV, there seems to be a slightly higher possibility of its formation with MPUV, particularly at the shorter UV wavelengths below 240nm.
Until now, however, it had not been established whether this posed any health risks.
Recent research in the USA has now shown that nitrite formation during MPUV disinfection is minimal and unlikely to be a health concern.
The researchers showed that, within the parameters of the experiments, the amount of nitrite formation was well below the U.S.
maximum level of 1 ppm.
They concluded that, under the present U.S.
regulations, nitrite formation poses no significant problem for water utilities using MPUV lamps.
These results are reassuring and underline the overall advantage of MPUV over LPUV.
Not only does MPUV have a wide, polychromatic output which damages microorganisms beyond repair, it also uses far fewer UV lamps than LPUV systems.
This means that the UV output from each lamp can be individually monitored, ensuring optimum dosing at all times.
It also simplifies operational and maintenance procedures, reduces headloss and means that significantly less Mercury (Hg) and other additives are present within the fluid stream, reducing the risk to the environment.
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