Julian L. Fairey

Improving on SUVA254 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.

Improved (and Singular) Disinfectant Protocol for Indirectly Assessing Organic Precursor Concentrations of Trihalomethanes and Dihaloacetonitriles

Measurements of disinfection byproduct (DBP) organic precursor concentrations (OPCs) are crucial to assess and improve DBP control processes. Typically, formation potential tests - specified in Standard Methods (SM) 5710-B/D - are used to measure OPCs. Here, we highlight several limitations of this protocol for dihaloacetonitriles and trihalomethanes and validate a novel Alternative Method (AM). The effects of pH, disinfectant type (free chlorine and monochloramine), and chlor(am)ine residual (CR) were examined on DBP formation in a suite of waters. Using the SM, DHAN decreased 43-47% as the CR increased from 3 to 5 mg L(-1) as Cl2, compromising OPC assessments. In contrast, a high monochloramine dose (250 mg L(-1) as Cl2) at pH 7.0 (the AM) accurately reflected OPCs. The two methods were compared for assessing DBP precursor removal through three granular activated carbon (GAC) columns in series. Breakthrough profiles assessed using the AM only showed DBP precursor sorption occurred in each column that decreased over time (p = 0.0001). Similarly, the AM facilitated ranking of three types of GAC compared in parallel columns, whereas the SM produced ambiguous results. Fluorescence intensity of a humic-like fluorophore (i.e., I345/425) correlated strongly to precursor removal in the GAC columns. The practical implications of the results are discussed.

Emerging investigators series: trihalomethane, dihaloacetonitrile, and total N-nitrosamine precursor adsorption by modified carbon nanotubes (CNTs) and CNT micropillars

Carbon nanotubes (CNTs) have been previously shown to adsorb organic precursors of disinfection byproducts (DBPs), including trihalomethanes (THMs), dihaloacetonitriles (DHANs), and total N-nitrosamines (TONO). The goal of this study is to elucidate CNT physical and chemical properties that enhance DBP precursor adsorption and provide proof-of-concept evidence to support a novel CNT-based application mode. Batch sorption data with varying CNT types, doses, and pH were analyzed with numerical models which revealed specific surface area controlled adsorption of THM and DHAN precursors and cumulative pore volume and surface oxygen content controlled adsorption of TONO precursors. To facilitate assessment of TONO precursors in low flow continuous flow sorption systems, a surrogate was developed using metrics from asymmetric flow field-flow fractionation with inline fluorescence detection and whole water fluorescence excitation-emission matrices (R2 = 0.576). Using this surrogate, we showed that affixed, CNT micropillars were capable of sorbing TONO precursors in continuous flow systems. These findings inform future modification of CNTs and provide proof-of-concept for development of structured CNT bundles for enhanced adsorption of TONO precursors.