Nitrite Quantification by Second Derivative Chemometric Models Mitigates Natural Organic Matter Interferences under Chloraminated Drinking Water Distribution System Conditions

Nitrite (NO2-) production in chloraminated drinking water distribution systems (CDWDSs) is among the first bulk water indicators of a nitrification event and is typically quantified using ion chromatography (IC) or colorimetric techniques. NO2- can also be quantified using chemometric models (CMs) formulated using molar absorptivity (6) and/or ultraviolet absorbance (UVA) spectra, 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 demonstrate that the impact of NOM was mitigated in the second derivative molar absorptivity (6 '') and UVA spectra (UVA '') between 200-300 nm and developed a generalizable CM for NO2- quantification. The 6 ''+UVA '' CM was 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 6 ''+UVA '' CM used 6 '' for NO2-, nitrate (NO3-), Br-, and NH2Cl at wavelengths of 213-, 225-, 229-and 253 nm, had an adjusted 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 NOM types and Br- indicated the 6 ''+UVA '' CM was generalizable at NOM concentrations like those in the BAR tests (<= 2.5 mg.L-1-C). The 6 ''+UVA '' CM accurately simulated NO2- in field tests from two CDWDSs undergoing nitrification, including one with NOM at 3.5 mg.L-1-C, illustrating a practical application of the CM for identifying biological ammonia oxidation.

Automated summary

Nitrite (NO2-) production in chloraminated drinking water distribution systems (CDWDSs) can be quantified using chemometric models (CMs) formulated using molar absorptivity (6) and/or ultraviolet absorbance (UVA) spectra. The accuracy and generalizability of these models are a concern due to variations in source water properties. This study developed a generalizable CM for NO2- quantification that mitigated the impact of source water organic matter and validated its accuracy in field tests.