Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Karanfil, Tanju

Committee Member

Freedman , David

Committee Member

Lee , Cindy

Abstract

Ever since toxic disinfection by-products (DBPs) were discovered in the 1970s drinking water utilities have had to continue to develop treatment strategies to reduce the acute health risk from infectious pathogens in water, and at the same time limit the formation of disinfection by-products. The recent two stage (1998, 2006) D/DBP rule enacted by the Environmental Protection Agency (EPA) which sets limits of 80 µg/L for trihalomethanes (THMs) and 60 µg/L for haloacetic acids (HAAs) will likely put more pressure on utilities in the future to decrease their chorine contact time and follow that with ammonia addition to form monochloramine because chloramination practices form fewer THMs and HAAs.
Generally, iodinated DBPs are the most toxic DBPs followed by the brominated and chlorinated DBPs. Because monochloramine practices favor the formation of iodinated DBPs, there are increasing concerns that utilities may be forming more toxic iodinated DBPs such as iodinated trihalomethanes (I-THMs).
The main objective of this research was to investigate I-THM formation and control during water treatment for a realistic Br-/I- mass ratio of 10, at two representative bromide/iodide levels [(i) 200 µg/L and 20 µg/L, and (ii) 800 µg/L and 80 µg/L] encountered in source waters. Unfortunately, previous I-THM research often neglected this very important Br-/I- ratio because iodide was often added in much higher concentrations than bromide. Specifically, this research project focused on three main sub-objectives: (i) to investigate and compare I-THM formation from preformed monochloramine and prechlorination followed by ammonia addition, (ii) to evaluate three commonly used preoxidants in water treatment (potassium permanganate, chlorine dioxide, and hydrogen peroxide) for controlling I-THM formation, and (iii) to investigate the importance of bromide to iodide ratio in I-THM formation and speciation from preformed monochloramine and preoxidation.
The results showed that for preformed monochloramine, I-THM formation was more favorable in low-SUVA waters than high-SUVA waters. On the other hand, for prechlorination followed by ammonia addition, high-SUVA waters generally formed higher concentrations of I-THMs than low-SUVA waters. For preformed monochloramine, generally higher I-THM and THM formation was observed at lower pH. However, if the iodide concentration was high (>80 µg/L), significant iodoform (CHI3) formation was sometimes observed at higher pH. For prechlorination, it was shown that increases in Cl2/DOC ratio and Cl2/I- ratio decreased I-THM formation, but increased THM formation. Overall, significant differences in I-THM speciation for preformed monochloramine and prechlorination were observed.
The results for preoxidation showed that potassium permanganate and hydrogen peroxide were unsuccessful in reducing I-THM formation. Chlorine dioxide showed promising results for reducing I-THM formation for high iodide concentrations (>80 µg/L) because iodoform (CHI3) formation sometimes decreased with increasing preoxidation dose. In some cases, I-THM formation was enhanced from preoxidation.

Investigations into the importance of bromide to iodide ratio showed that I-THM yields and speciation formed from preformed monochloramine and preoxidants will depend significantly on bromide to iodide ratios and concentrations.

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