Ordering Information:
ORDER NUMBER:  91209
DATE AVAILABLE: Winter 2007/2008

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PRINCIPAL INVESTIGATORS:
Frank Sacher, Carsten K. Schmidt, Changha Lee, and Urs von Gunten

OBJECTIVES:
The objectives of the project were to identify strategies that could be used by water utilities to minimize the formation of carcinogenic nitrosamines during disinfection of drinking water. Additionally, the relevance of other nitrosamines besides N-nitrosodimethylamine (NDMA) for drinking water disinfection with chloramine was assessed.

BACKGROUND:
NDMA is an aliphatic nitrosamine that has been identified as a disinfection by-product during chloramination of drinking water. In the United States, it has been detected in water treatment plants using chloramine as a disinfectant. NDMA has significant health concerns, as its 10^-6 cancer-risk level was determined at a level of 0.7 ng/L. Although other nitrosamines exhibit a similar toxicological profile, their relevance for drinking water disinfection with chloramine is unclear.

HIGHLIGHTS:
Compared to NDMA, the formation of other nitrosamines during chloramination is of minor relevance. The following options for minimizing NDMA formation during chloramination were identified:

• Avoiding using source waters that are characterized by high wastewater loads
• Removing precursor compounds by microbiological treatment (slow sand filtration, artificial groundwater recharge, or riverbank filtration) or by a pre-oxidation step (pre-ozonation or pre-chlorination)
• Optimizing operational parameters (decreasing disinfectant dose, lowering pH, use of chlorine instead of chloramine, production of chloramine in a manner that minimizes the concentration of dichloramine [e.g., by addition of free chlorine before ammonia]).

APPROACH:

Literature Survey
An extensive literature search was performed to collect information on mechanisms of nitrosamine formation, to identify or at least characterize possible precursors for nitrosamine formation, and to identify tools for removal of precursor compounds prior to disinfection. Finally, possibilities for nitrosamine removal were evaluated.

Laboratory-Scale Experiments
Additional laboratory-scale experiments were performed in order to fill knowledge gaps identified during the literature survey. For this, tests for the determination of the nitrosamine formation potential (NFP) were performed. With these NFP tests, water samples could be characterized with regard to their potential to form nitrosamines.

Full-Scale Tests
The conclusions from the literature survey and the laboratory-scale experiments were verified by full-scale tests in water utilities in the United States, Australia, and Germany.

RESULTS/FINDINGS:

Formation of Nitrosamines
The formation of many other nitrosamines during chloramination is almost negligible compared to the formation of NDMA.

Precursors
Most of the precursors for nitrosamine formation during chloramination can be related to anthropogenic sources. Results from laboratory-scale experiments clearly demonstrated that structures with a dimethylamine group being coupled over a methylene group in a-position to an electron-rich, heterocyclic, 5-membered ring system (e.g., furan or thiophene) typically form NDMA with very high conversion rates. Ranitidine, a pharmaceutical, showed extraordinary high conversion efficiency. Effective options for removal of nitrosamine precursors are biodegradation, oxidation (with either ozone or chlorine), and GAC filtration while aeration, lime softening, or coagulation/flocculation turned out to be rather ineffective.

Minimizing Nitrosamine Formation
Besides precursor removal, optimization of operational parameters is a promising option for minimizing nitrosamine formation during chloramination. Effective options include reduction of disinfectant dose, lowering of pH, use of chlorine instead of chloramine, and minimizing dichloramine levels during disinfection, e.g., by addition of free chlorine before ammonia. Pre-oxidation steps can be very effective in reducing NDMA formation during chloramination, if carefully optimized with respect to location, dose of oxidant, contact time, and pH.

IMPACT:
The outcomes of the project will enable water utilities that use chloramination for disinfection purposes to minimize the nitrosamine levels in their drinking water and thus will facilitate to comply with existing or future drinking water standards. Minimizing drinking water concentrations of the carcinogenic nitrosamines is also a significant contribution to improving consumers’ health. The project provided information on the identity of a relevant precursor compound for NDMA formation that can act as a first step towards the elimination of this unwanted compound.

RESEARCH PARTNER:
TZW-Germany

PARTICIPANTS:
Five U.S. utilities, one Australian utility, and three German utilities participated in the full-scale testing phase of the project.