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 (Ɛ) 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 (Ɛ″) and UVA spectra (UVA″) between 200-300 nm and developed a generalizable CM for NO2- quantification. The Ɛ″+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 Ɛ″+UVA″ CM used Ɛ″ 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 Ɛ″+UVA″ CM was generalizable at NOM concentrations like those in the BAR tests (≤ 2.5 mg·L-1-C). The Ɛ″+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.

Suitability of Organic Matter Surrogates to Predict Trihalomethane Formation in Drinking Water Sources.

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 (UV254), fluorescence excitation/emission wavelength pairs (IEx/Em), and the maximum fluorescence intensities (FMAX) 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, UV254, IEx/Em, and FMAX 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 UV254 was stronger (r2=0.89) than I240/562 (r2=0.81, the strongest surrogate parameter from excitation/emission matrix pair picking), FMAX from a humic/fulvic acid-like PARAFAC component (r2=0.78), and DOC (r2=0.75). Results indicate that UV254 was the most accurate TTHMFP precursor surrogate parameter assessed for a diverse group of raw and alum-coagulated waters.

Assessing trichloromethane formation and control in algal-stimulated waters amended with nitrogen and phosphorus.

Nitrogen (N) and phosphorus (P) enrichments can stimulate algal growth in drinking water sources, which can cause increased production of disinfection byproduct (DBP) precursors. However, the effect of systematic N and P enrichments on DBP formation and control has not been adequately studied. In this work, we enriched samples from a drinking water source - sampled on April 5, May 30, and August 19, 2013 - with N and P to stimulate algal growth at N : P ratios covering almost five orders of magnitude (0.2-4429). To simulate DBP-precursor removal processes at drinking water treatment plants (DWTPs), the samples were treated with ClO2 followed by alum coagulation prior to free chlorine addition to assess the DBP formation potential (FP). Trichloromethane (TCM) was the predominant DBP formed and the TCMFP was the highest at intermediate N : P molar ratios (∼10 to 50), which corresponded with the peak in algal biomass, as measured by chlorophyll-a (Chl-a). Algal biomass was P-limited throughout the study period, and co-limited by N for the August 19 sampling set. The differences in TCMFP between the raw and treated waters decreased with increasing P amendment, indicating that ClO2 and alum coagulation became less effective for TCM precursor removal as algal biomass increased. This study highlights the impact of nutrient enrichments on TCM formation and control and has implications for nutrient management strategies related to source water protection and for DWTPs that use source waters increasingly enriched with N and P.

Improving on SUVA 254 using fluorescence-PARAFAC analysis and asymmetric flow-field flow fractionation for assessing disinfection byproduct formation and control.

Several challenges with disinfection byproduct (DBP) control stem from the complexity and diversity of dissolved organic matter (DOM), which is ubiquitous in natural waters and reacts with disinfectants to form DBPs. Fluorescence parallel factor (PARAFAC) analysis and asymmetric flow-field flow fractionation (AF4) were used in combination with free chlorine DBP formation potential (DBPFP) tests to study the physicochemical DOM properties and DBP formation in raw- and alum-coagulated waters. Enhanced coagulation with alum became more effective at removing DBP-precursors as the pH decreased from 8 to 6. AF4-UV(254) fractograms indicated enhanced coagulation at pH 6 preferentially removed larger DOM, whereas no preferential size removal occurred at pH 8. Fluorescence-PARAFAC analysis revealed the presence of one protein-like and three humic-like fluorophore groups; stronger linear correlations were found between chloroform and the maximum intensity (F(MAX)) of a humic-like fluorophore (r(2) = 0.84) than with SUVA(254) (r(2) = 0.51). This result indicated that the fluorescence-PARAFAC approach used here was an improvement on SUVA(254), i.e., fluorescence-based measurements were stronger predictors of chloroform formation.

Coupling asymmetric flow-field flow fractionation and fluorescence parallel factor analysis reveals stratification of dissolved organic matter in a drinking water reservoir.

Using asymmetrical flow field-flow fractionation (AF4) and fluorescence parallel factor analysis (PARAFAC), we showed physicochemical properties of chromophoric dissolved organic matter (CDOM) in the Beaver Lake Reservoir (Lowell, AR) were stratified by depth. Sampling was performed at a drinking water intake structure from May to July 2010 at three depths (3-, 10-, and 18-m) below the water surface. AF4-fractograms showed that the CDOM had diffusion coefficient peak maximums between 3.5 and 2.8 x 10⁻6 cm² s⁻¹, which corresponded to a molecular weight range of 680-1950 Da and a size of 1.6-2.5 nm. Fluorescence excitation-emission matrices of whole water samples and AF4-generated fractions were decomposed with a PARAFAC model into five principal components. For the whole water samples, the average total maximum fluorescence was highest for the 10-m depth samples and lowest (about 40% less) for 18-m depth samples. While humic-like fluorophores comprised the majority of the total fluorescence at each depth, a protein-like fluorophore was in the least abundance at the 10-m depth, indicating stratification of both total fluorescence and the type of fluorophores. The results present a powerful approach to investigate CDOM properties and can be extended to investigate CDOM reactivity, with particular applications in areas such as disinfection byproduct formation and control and evaluating changes in drinking water source quality driven by climate change.