WATER:
Raw Water Quality:
Water quality plays an important role in the UV disinfection process.
Chemicals and substances in the water may impact UV transmittance. Higher
UVT water needs fewer lamps and power to achieve a specified UV dose.
Cushing et al. (2001) studied the UV absorption properties of several
common water treatment chemicals. Based on experiments they concluded
that ammonia, ammonium ion, calcium ion, ferrous iron ion, hydrogen
peroxide, hydrogen ion, hypochlorite ion, magnesium ion, manganese ion,
permanganate ion, phosphate species, sulfate ion, sulfite ion, and zinc
ion had insignificant effects on UV transmittance. Dissolved inorganic
compounds have little influence on UV transmittance although hypochlorite
and chloramines show a higher absorbance. However Cushing et al. found
that ozone and ferric iron could significantly reduce transmittance.
Ozone should only be an issue in situations where ozone does not have
a chance to dissipate or is not quenched prior to the UV reactor. If
ferrous iron is present such as in some ground water systems, ferrous
oxidation should be inhibited. Jeskey et al. (2001) also reports that
humic acids, phenolic compounds, lignin sulfonates, copper, iron, and
compounds that color water tend to absorb UV light and decrease UV transmission.
Pretreatment may be necessary to reduce these. Particles in the water
can have a negative affect on the effectiveness of the UV disinfection
treatment. The UV intensity can be reduced by particles scattering the
UV light. Particles can also block microorganisms from UV light reducing
treatment performance. Maggi (2001) states that pH, temperature, alkalinity,
and total inorganic carbon do not appear to impact the overall effectiveness
of UV disinfection. A caveat by others is about water quality leading
to fouling of quartz sleeves or causing bacteria to aggregate into particulates.
Due to these water quality issues, filtered water is the most appropriate
application for UV disinfection.
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