Grantee Research Project Results
2000 Progress Report: Mechanisms and Kinetics of Chloramine Loss and By-Product Formation in the Presence of Reactive Drinking Water Distribution System Constituents.
EPA Grant Number: R826832Title: Mechanisms and Kinetics of Chloramine Loss and By-Product Formation in the Presence of Reactive Drinking Water Distribution System Constituents.
Investigators: Valentine, Richard L.
Institution: University of Iowa
EPA Project Officer: Hahn, Intaek
Project Period: September 15, 1998 through September 14, 2001
Project Period Covered by this Report: September 15, 1999 through September 14, 2000
Project Amount: $317,868
RFA: Drinking Water (1998) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The fate of chloramines in drinking water distribution systems, the nature of the reactions and by-products, as well as factors that influence these are largely unknown. Recent exploratory work at the University of Iowa indicates the potential importance of several ubiquitous reactive distribution system components. These substances include natural organic matter (NOM), reduced iron and manganese, iron oxides, bromide, nitrite, and oxygen. This project seeks to enhance our understanding of the influence of these reactive substances on: (1) the fate of monochloramine and the nature of inorganic reaction products; (2) the kinetics of monochloramine loss; and (3) the formation of selected organic disinfection by-products (DBPs). Results will also be used to (4) extend existing mechanistic chloramine reaction models to include the effects of these reactive substances.Progress Summary:
Work has progressed in several areas. These include: (1) measuring and modeling chloramine and free chlorine loss from reaction with NOM and pipe deposits, (2) evaluating and modeling the stability of monochloramine in the presence of nitrite, (3) evaluating the stability of HAAs and nitrite in the presence of ferrous hydroxide, and (4) investigating the formation of nitrosodimethylamine via a reaction involving monochloramine and a model organic nitrogen precursor.
Monochloramine reacts slowly with NOM obtained from a variety of sources. Most of this loss can be attributed to relatively simple reduction reactions, not substitution to form organic DBPs. The reaction is characterized by a relative fast and slow biphasic reaction. Modeling efforts are directed toward evaluation of the applicability of one- and two-site reaction models involving a direct reaction with monochloramine. Preliminary results suggest that the reactivity correlates with absorbance at 254 nm and that a one-site reaction model is not adequate to describe monochloramine loss in the presence of NOM. It is suspected that complexation with some reduced metal also may contribute to the biphasic behavior.
Preliminary work on the influence of oxygen on the reaction of monochloramine with deposit material containing reduced iron has been inconclusive.
Nitrite is an inorganic DBP believed to be produced by biological oxidation of ammonia in chloraminated systems. The stability of nitrite in the presence of monochloramine was successfully modeled by consideration of its oxidation to nitrate by monochloramine via a direct reaction. Experimental results verify that the reaction can be slow, so that both monochloramine and nitrite may coexist depending on water quality characteristics.
Several important DBPs are reactive with reduced iron oxides believed to be important distribution system constituents. Three HAAs were transformed by ferrous hydroxide at pH 7. The fastest and most extensive decay was observed for monobromoacetic acid. Dichloroacetic acid was the most stable. This may explain why it is frequently observed in distribution systems. In somewhat of a contrast to the HAAs, only brominated THMs were observed to be reactive in the presence of ferrous hydroxide. No loss of chloroform was observed up to 10 g Fe/L ferrous hydroxide content and up to 24 hours contact compared to essentially complete loss of bromodichloromethane and bromoform after 2 hours contact at 3 g/L ferrous hydroxide.
N-nitrosodimethylamine (NDMA) is a drinking water contaminant of emerging concern at the nanogram-per-liter level. It is generally believed that it is formed via a reaction of nitrite and an organic nitrogen-containing precursor (such as dimethylamine). Our initial studies indicate that it also is probably formed by a direct reaction involving monochloramine. If so, NDMA should be considered a "new" disinfection by-product.
Future Activities:
We are continuing our efforts at modeling monochloramine decay in the presence of NOM, nitrite, and other constituents. We also are conducting parallel studies on HAA formation. NDMA studies are focusing on: (1) improved analytical capabilities, and (2) reaction kinetics and mechanism studies.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 15 publications | 8 publications in selected types | All 8 journal articles |
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Type | Citation | ||
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Vikesland PJ, Ozekin K, Valentine RL. Monochloramine decay in model and distribution system waters. Water Research 2001;35(7):1766-1776. |
R826832 (2000) R826832 (Final) |
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Supplemental Keywords:
drinking water, disinfection, disinfection by-products., RFA, Scientific Discipline, Water, Chemical Engineering, Environmental Chemistry, Chemistry, Drinking Water, microbial contamination, public water systems, oxidation, disinfection byproducts (DPBs), community water system, kinetics of Chloramine loss, treatment, bromate formation, brominated DPBs, manganese, drinking water distribution system, iron, microbial risk management, chloramines, emerging pathogens, DBP risk management, water quality, drinking water contaminantsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.