UV Photolysis of Nitrate:  Effects of Natural Organic Matter and Dissolved Inorganic Carbon and Implications for UV Water Disinfection

Nitrite (NO2 -) formation during ultraviolet (UV) photolysis of nitrate was studied as a function of pH and natural organic matter (NOM) concentration to determine water-quality effects on quantum yields and overall formation potential during UV disinfection of drinking water with polychromatic, med...

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Bibliographic Details
Published in:Environmental science & technology 2001-07, Vol.35 (14), p.2949-2955
Main Authors: Sharpless, Charles M, Linden, Karl G
Format: Article
Language:English
Subjects:
Applied sciences
Carbon
Carbon - analysis
Disinfection - methods
Drinking water and swimming-pool water. Desalination
Environmental impact
Exact sciences and technology
Mercury
Nitrates
Nitrates - analysis
Nitrates - chemistry
Photolysis
Pollution
Pressure
Ultraviolet radiation
Ultraviolet Rays
USA
Water
Water Purification
Water treatment and pollution
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Summary:Nitrite (NO2 -) formation during ultraviolet (UV) photolysis of nitrate was studied as a function of pH and natural organic matter (NOM) concentration to determine water-quality effects on quantum yields and overall formation potential during UV disinfection of drinking water with polychromatic, medium-pressure (MP) Hg lamps. Quantum yields measured at 228 nm are approximately 2 times higher than at 254 nm under all conditions studied. In the absence of NOM, NO2 - quantum yields decrease with time. With addition of NOM, initial quantum yields increase, and the time-dependent decrease is eliminated. At 15 ppm dissolved organic carbon (DOC) as NOM, the quantum yield increases with time. Dissolved inorganic carbon significantly decreases NO2 - yields at pH 8 but not pH 6, presumably by reaction of CO2(aq) with peroxynitrite, a major intermediate in NO2 - formation. The results indicate important and previously unrecognized roles for NOM and CO2(aq) in nitrate photolysis. When photolysis was carried out using the full spectrum MPUV lamp and germicidally relevant UV doses, NO2 - concentrations remained well below the U.S. maximum contaminant level of 1 ppm N, even with nitrate initially present at 10 ppm N. Under current U.S. regulations, NO2 - formation should not pose a significant problem for water utilities during UV disinfection of drinking water with MP Hg lamps.
ISSN:0013-936X
1520-5851
DOI:10.1021/es002043l