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Chloramination of Concentrated Drinking Water: Evaluation of Disinfection Byproduct Formation and Dosing Scenarios - Portland
Citation:
Kennicutt, A., P. Rossman, J. Bollman, G. Abulikemu, T. Aho, C. Wu, B. Park, M. Sasakura, Y. Ye, G. Onstad, D. Wahman, AND J. Pressman. Chloramination of Concentrated Drinking Water: Evaluation of Disinfection Byproduct Formation and Dosing Scenarios - Portland. Presented at American Water Works Association Water Quality Technology Conference, Portland, OR, November 12 - 16, 2017.
Impact/Purpose:
This research will be of interest to engineers, scientists, and operators of drinking water systems that use chloramines as a secondary disinfectant
Description:
Complex mixtures of disinfection by-products (DBPs) are formed when the disinfectant oxidizes constituents (e.g., natural organic matter (NOM) and organic pollutants) found in the source water. Since 1974, over 600 DBPs have been identified in drinking water. Despite intense identification efforts, greater than 50% of the total organic halogen (TOX) formed during disinfection remains unidentified. Concerns for public health continue to drive DBP research as increased exposure has shown to have carcinogenic and/or endocrine disrupting properties. The estimated potency of DBPs investigated either individually or in defined mixtures does not account for the magnitude of effects reported in the positive epidemiologic studies, suggesting the need for toxicological evaluation of whole DBP mixtures, including the unidentified DBPs. Previously, a procedure was developed to chlorinate concentrated NOM solutions to create whole mixtures of DBPs representative of free chlorine systems that was used for health effects research. Extending this previous work, the objective of this research was to create whole mixtures of concentrated DBPs representative of chloraminated systems. Ohio River water was collected post-ultrafiltration (UF1X, 2.01 mg total organic carbon (TOC)/L) and as reverse osmosis concentrate that had been concentrated 142-times the UF1X TOC concentration (CONC142X, 285 mg TOC/L). A portion of the CONC142X was freeze-dried to produce a dry, solid NOM that was reconstituted at defined TOC concentrations for experiments, representing 1-times (RECON1X), 142-times (RECONC142X), and 500-times (RECON500X, 1000 mg TOC/L) the UF1X TOC concentration. For experiments, the CONC142X was also diluted down to an equivalent 1X TOC concentration (CONC1X). In total, six waters were used in the experiments, consisting of three 1X (UF1X, CONC1X, and RECON1X), two 142X (CONC142X, RECON142X) and one 500X (RECON500X) water. For each experiment, bromide (1X = 115 μg/L) and iodide (1X = 11.5 μg/L) were added to a pH 8 phosphate buffered water. Subsequently, preformed chloramines (4.75:1 chlorine to ammonia-nitrogen ratio) were added. Prior to DBP experiments, initial experiments along with a chloramine kinetic model were used to establish initial chloramine concentrations and reaction times required for each water so that an equivalent (i.e., scaled to 1X) chloramine amount reacted with NOM: 1X (2.5 mg/L and 3 days), 142X (50 mg/L and 3 days), and 500X (180 mg/L and 2 days). The DBP experiment results highlight the complexity that chloramination chemistry introduces when trying to produce whole mixtures of DBPs that scale with TOC concentration, and these results provide the necessary information to establish how well chloramination of concentrated water samples are able to represent drinking water (i.e., 1X) conditions for future DBP toxicology studies. Results of initial and DBP experiments will be discussed.