Citation:

Do, T., A. Pifer, D. Wahman, R. Hickman, J. Chimka, AND J. Fairey. Nitrite Quantification by Second Derivative Chemometric Models Mitigates Natural Organic Matter Interferences under Chloraminated Drinking Water Distribution System Conditions. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 229:119430, (2023). https://doi.org/10.1016/j.watres.2022.119430

Impact/Purpose:

The environmental or health problem addressed by the study: Measurement of nitrite and nitrate in drinking water. A general description of the work and results: Experiments have been conducted to evaluate a new methodology to measure nitrite in drinking water. The long-term importance or significance of the findings: Provides online monitoring for nitrite in drinking water. Who would be interested in or could apply the results (e.g. program or regional partners, general public, local communities): Researchers and drinking water utilities trying to prevent nitrification in drinking water systems.

Description:

Nitrite (NO2−) produced during nitrification episodes in chloraminated drinking water distribution systems (CDWDSs) is typically quantified using ion chromatography (IC) or colorimetric techniques.  NO2− can also be quantified using chemometric models (CMs) formulated using molar absorptivity (?) and/or ultraviolet absorbance (UVA) spectra suitable for real-time measurements, but concerns exist regarding their accuracy and generalizability because of varying source water natural organic matter (NOM), monochloramine (NH2Cl), bromide (Br−), and other species in CDWDSs.  We demonstrated that second derivative molar absorptivity (?″) and UVA spectra (UVA″) were circa zero for three NOM types between 200–300 nm, whereas NO2− had a peak maximum of 11.9 L•mol−1•cm−1•nm−2 at 232 nm.  ?″+UVA″ and UVA″ CMs were calibrated with daily NO2− measurements by IC from five biofilm annular reactor (BAR) tests with feedwater from Fayetteville, Arkansas, USA (FAY1, n = 275) and validated with eight BAR tests (n = 376) with another Fayetteville water (FAY2) and two waters from Dallas, Texas, USA (DAL1 and DAL2).  The ?″+UVA″ CM used ?″ for NO2−, nitrate (NO3−), Br−, and NH2Cl and wavelengths of 213-, 225-, 229- and 253 nm; had an adjusted R2 (Adj-R2) of 0.992 for FAY1 and 0.987 for the other waters; and had a method detection limit (MDL) of 0.050 mg•L−1-N.  NO2− challenge samples with three reconstituted NOMs and Br− indicated the ?″+UVA″ CM was generalizable although inaccuracies manifested at greater NOM concentrations (3.5- and 5.0 mg•L−1-C) than in the BAR tests (0.3–2.2 mg•L−1-C).  In comparison, the UVA″ CM had three significant wavelengths (221-, 235-, and 253 nm), Adj-R2 of 0.998 for FAY1 following removal of nine influential observations (n = 266) and 0.991 for the other waters, and an MDL of 0.066 mg•L−1-N.  The UVA″ CM was biased by about 0.1 mg•L−1-N due to Br− at greater concentrations in the challenge samples compared to the BAR tests, illustrating the UVA″ CM was source water specific.  While ?″+UVA″ and UVA″ CMs accurately simulated NO2− concentrations in BAR tests and reliably indicated biological ammonia oxidation, the ?″+UVA″ CM was generalizable to conditions typical in CDWDSs.

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