Date of Award

Spring 1-1-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Karl Linden

Second Advisor

Fernando L. Rosario-Ortiz

Third Advisor

Aaron Dotson

Abstract

Although chlorine in water can be beneficial for disinfection, it is also a nuisance chemical for some industries such as microchip processing, pharmaceuticals manufacturing, and beverage companies. For these industrial processes, there is a need to dechlorinate the water using non-chemical based methods. Ultraviolet light (UV) can be used for both disinfection purposes and for chemical removal in municipal and industrial water supplies. The degradation of chlorine has been known to occur under both low-pressure (LP) and medium-pressure (MP) UV. When dissolved organic matter and other compounds such as nitrate are present in the water, enhanced degradation of chlorine occurs. The mechanisms associated with the enhanced chlorine degradation rates, primarily through the photolysis of chlorine and nitrate, were studied. The pH and related chlorine speciation was an important factor when examining the reactions taking place. Polychromatic light from MP UV sources was found to be much more effective at removing free chlorine when nitrate was present, with the fastest decay rates occurring at basic pH. Enhanced degradation of chlorine with nitrate present resulted from nitrite formation and radical production during the photolysis of nitrate with light below 240 nm. Nitrite reacts quickly with both chlorine and hydroxyl radicals, but these reactions are strongly dependent on the pH. These finding provide insight into the use of UV light in the ultrapure water industry.

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