Date of Award

8-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Karanfil, Tanju

Committee Member

Ladner , David A

Committee Member

Lee , Cindy

Abstract

Water treatment plants in the United States (US) have been switching from chlorination to chloramination in the search for a disinfection process to reduce formation of regulated disinfection by-products (DBPs). Unfortunately, the trade-off is the formation of N-nitrosamines. N-nitrosodimethylamine (NDMA) is the most commonly detected N-nitrosamine in US distribution systems. In the Integrated Risk Information Service (IRIS) database of the United States Environmental Protection Agency (USEPA), NDMA has been identified to have an estimated 10-6 lifetime cancer risk level at a concentration of 0.7 ng/L in drinking water. N-nitrosamines are currently not regulated by the USEPA; however, are listed on the Contaminant Candidate List 3 (CCL3). USEPA is in the process of a regulatory determination for NDMA in drinking water. As wastewater effluents become an increasing influence on surface waters and de facto water reuse becomes more common, the need to remove NDMA precursors becomes more urgent. Furthermore, low pressure UV lamps used for disinfection in wastewater treatment have been shown to have minimal effect on the removal of NDMA precursors. In fact, the increasing trend of switching from chlorine to UV disinfection at many wastewater treatment plants can be one reason for the increasing influence of wastewater effluents on downstream water treatment plants for NDMA formation. The use of oxidants in wastewater could be used to reduce the release of NDMA precursors into surface waters. Chlorine, ozone, and chlorine dioxide have been shown to vary in their effectiveness on removing NDMA precursors. The first objective in this study was to compare chlorine to UV disinfection on removing NDMA precursors. Ten wastewater treatment plants were sampled before and after UV or chlorine disinfection. The UV disinfection results confirmed the findings in the literature and showed minimal removal. On the other hand, chlorine was found to have varying effectiveness. Plants low in ammonia concentration (0.8 mg/L) showed low removal at low doses; however, as dose increased, so did the removal. Further tests of five plants from the previous ten provided similar results, confirming that ammonia concentration directly affects removal of NDMA precursors. Increasing the chlorine dose consumes the ammonia, leaving free chlorine to oxidize NDMA precursors. The second objective was to examine the effectiveness of ozone, chlorine dioxide, and UV for the control of NDMA precursors. Effluents from two municipal wastewater treatment plants, one with high ammonia and the other with low ammonia concentrations, were compared. Ozone showed almost complete removal of NDMA precursors (~95%) in the presence and absence of ammonia. Chlorine dioxide exhibited variable degree of NDMA precursor removals (19-90%) depending on the dose. UV showed little to no removal which was expected. The third objective examined the influence of the oxidants on the NDMA precursor once discharged from a wastewater treatment plant. Chlorine, ozone, chlorine dioxide, UV, and a control (i.e., no oxidant or UV) were tested in simulated batch natural attenuation experiments to assess how NDMA precursors are behaving in natural systems. The most change occurred with the effluent UV and the control. UV showed initially to have minimal removal of NDMA precursors which follows literature and previous objectives in this research; however, it did degrade 50% by day 7 and then 73% by day 20. The control showed similar trends with a degrade in NDMA precursors at 50% at day 7 and then 82% by day 20. Since oxidants chlorine (in the presence of low ammonia), chlorine dioxide, and ozone were able to remove large amount of NDMA precursors, there was minimal change after entering the simulated natural system. Overall, a small dose (much lower than required for disinfection) of chlorine, ozone, and chlorine dioxide could be used in wastewater treatment plants for the removal of NDMA precursors which would benefit downstream water treatment plants and future applications of water reuse for NDMA control. The effectiveness of ozone and chlorine dioxide will not be sensitive to background ammonia levels whereas for chlorine to be as effective, first the background ammonia demand needs to be satisfied. This research showed that NDMA control strategies require a holistic approach, and the solution may be more feasible to address at the upstream wastewater treatment plants rather than downstream impacted water treatment plants and distribution systems.

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