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The N-nitrosodimethylamine (NDMA) formation pathway in chloraminated drinking water remains unresolved. In pH 7–10 waters amended with 10 μM total dimethylamine and 800 μeq Cl2·L–1 dichloramine (NHCl2), NDMA, nitrous oxide (N2O), dissolved oxygen (DO), NHCl2, and monochloramine (NH2Cl) were kinetically quantified. NHCl2, N2O, and DO profiles indicated that reactive nitrogen species (RNS) formed during NHCl2 decomposition, including nitroxyl/nitroxyl anion (HNO/NO–) and peroxynitrous acid/peroxynitrite anion (ONOOH/ONOO–). Experiments with uric acid (a ONOOH/ONOO– scavenger) implicated ONOOH/ONOO– as a central node for NDMA formation, which were further supported by the concomitant N-nitrodimethylamine formation. A kinetic model accurately simulated NHCl2, NH2Cl, NDMA, and DO concentrations and included (1) the unified model of chloramine chemistry revised with HNO as a direct product of NHCl2 hydrolysis; (2) HNO/NO– then reacting with (i) HNO to form N2O, (ii) DO to form ONOOH/ONOO–, or (iii) NHCl2 or NH2Cl to form nitrogen gas; and (3) NDMA formation via ONOOH/ONOO– or their decomposition products reacting with (i) dimethylamine (DMA) and/or (ii) chlorinated unsymmetrical dimethylhydrazine (UDMH-Cl), the product of NHCl2 and DMA. Overall, updated NHCl2 decomposition pathways are proposed, yielding (1) RNS via and (2) NDMA via .

Broadly applicable disinfection by-product (DBP) precursor surrogate parameters could be leveraged at drinking water treatment plants (DWTPs) to curb formation of regulated DBPs, such as trihalomethanes (THMs). In this study, dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV 254 ), fluorescence excitation/emission wavelength pairs (I Ex/Em ), and the maximum fluorescence intensities (F MAX ) of components from parallel factor (PARAFAC) analysis were evaluated as total THM formation potential (TTHMFP) precursor surrogate parameters. A diverse set of source waters from eleven DWTPs located within watersheds underlain by six different soil orders were coagulated with alum at pH 6, 7, and 8, resulting in 44 sample waters. DOC, UV 254 , I Ex/Em , and F MAX values were measured to characterize dissolved organic matter in raw and treated waters and THMs were quantified following formation potential tests with free chlorine. For the 44 sample waters, the linear TTHMFP correlation with UV 254 was stronger (r 2 = 0.89) than I 240/562 (r 2 = 0.81, the strongest surrogate parameter from excitation/emission matrix pair picking), F MAX from a humic/fulvic acidlike PARAFAC component (r 2 = 0.78), and DOC (r 2 = 0.75). Results indicate that UV 254 was the most accurate TTHMFP precursor surrogate parameter assessed for a diverse group of raw and alum-coagulated waters.

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This research evaluated the effect of granular activated carbon (GAC) type and source water characteristics on steady‐state monochloramine reduction in fixed‐bed reactors (FBRs) under drinking water treatment conditions. Five commercially available GACs and two background waters were used to study monochloramine reduction in laboratory‐scale column studies. Steady‐state monochloramine destruction increased with decreasing water pH (over the range likely in chloramination, i.e., pH 7–9) regardless of GAC type or source water. A previously developed finite element model was verified experimentally for monochloramine influent concentrations of interest in drinking water (2 mg/L as Cl2). Simulation of steady‐state process performance with GAC particle sizes used in practice was performed using the model after it was calibrated to results from the monochloramine FBR studies. These steady‐state simulations indicate that with at least one of the GACs tested, < 8 min of empty bed contact time (EBCT) was required to meet the monochloramine standard for kidney dialysis water (0.1 mg/L as Cl2). Despite a required EBCT as long as 20 min, use of more‐traditional GACs may also be feasible for kidney dialysis, provided that benefits gained by steady‐state operation (i.e., never having to replace the filter media) outweigh filter size and portability considerations.

Steady-state monochloramine reduction in fixed-bed reactors (FBRs) was quantified on five types of granular activated carbon (GAC) using two background waters-one natural source water (LAW) containing 2.5-3.5 mg/L organic carbon and one synthetic organic-free water (NW). While more monochloramine was reduced at steady-state using NW compared to LAW for each GAC and empty-bed contact time studied, the differences in removal varied considerably among the GACs tested. Physical characterization of the GACs suggested that the degree of interference caused by natural organic matter (NOM) increased with increasing GAC surface area contained within pores greater than 2 nm in width. Acid/base and electrostatic properties of the GACs were not found to be significant in terms of NOM uptake, which indicated that size exclusion effects of the GAC pores overwhelmed the impact of the GAC surface chemistry. Therefore, selection of GAC to limit the impact of NOM on monochloramine reduction in FBRs should be based on pore size distribution alone, with the impact of NOM decreasing with decreasing mesoporosity and macroporosity.

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