Mechanisms and Kinetics of Chloramine Loss and By-Product Formation in the Presence of Reactive Drinking Water Distribution System Constituents.EPA Grant Number: R826832
Title: 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: Nolt-Helms, Cynthia
Project Period: September 15, 1998 through September 14, 2001
Project Amount: $317,868
RFA: Drinking Water (1998) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
The fate of chloramines in drinking water distribution systems, the nature of the reactions and by-products, as well as factors which influence these are largely unknown. Work is especially needed to elucidate the role of reactive substances on the fate of chloramines and on DBP formation. Recent exploratory work at Iowa indicates the importance of several ubiquitous reactive distribution system components in determining these. This project seeks to better characterize the influence of NOM, complexed and uncomplexed Fe and Mn, model and collected pipe deposit material, bromide ion, and oxygen on: 1) the fate of monochloramine and the nature of inorganic reaction products, 2) the kinetics of monochloramine chloramine loss, and 3) the formation of selected organic DBPs. Results will also be used to: 4) extend an existing mechanistic chloramine reaction model to include the effects of these reactive substances on chloramine loss and DBP formation.
The presence of these substances will generally increase the rate of chloramine loss and will affect the nature of the inorganic and organic disinfection by-products. Reactions involving NOM and reduced metals will be the dominant chloramine loss pathways in distribution systems containing deposit material. Deposit material will catalyze decomposition and some DBP formation reactions due to the presence of adsorbed reduced metals and NOM. Reduced iron and oxygen will increase chloramine decomposition and organic DBP formation through synergistic effects caused by a one electron transfer from monochloramine to produce a highly reactive radical. Bromide oxidation, while slow, will also enhance oxidation of NOM and brominated DBP formation. The effects of these constituents at different values of pH and Cl/N can be rationalized and predicted in terms of fundamental reactions.
The overall approach is to study simultaneous chloramine loss and DBP formation to provide a comprehensive picture of the fate and effects of chloramines. Studies will be conducted using collected and laboratory prepared water in batch reactors to assess the influence of aqueous phase constituents. Reactions involving whole pieces of authentic pipe deposit material will also be studied in a recirculating tubular reactor to better mimic the fluid flow in pipes. Constituent concentrations will be systematically varied as will be monochloramine concentration, pH, and the Cl/N ratio. Variations will include investigations of the effect of prechlorination and preozonation of the waters. Monochloramine concentrations will be measured over a period of at least five days. Samples will be taken for analysis of selected DBPs which may include chloropicrin, cyanogen chloride, cyanogen bromide, THMs, TOX, and haloacetic acids. Mass and redox balances will be made on all inorganic products including nitrogen gas, nitrate, nitrite, chloride, bromide,bromate, and ammonia. Results will be analyzed in the context of an existing mechanistic description of the reactions responsible for the autodecomposition of monochloramine.