BOOK OF ABSTRACTS 97 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL45 Fractionation and Characterization of Acids and Neutrals in Treated Wastewater Paul Westerhoff1, Leonie Minault1,2, Joshua Quinn1 1 Arizona State University and 2 École Supérieure de Chimie Physique Électronique de Lyon Effluent organic matter (EfOM) has become an increasingly important component of the aquatic carbon cycle due to the widespread discharge and reuse of treated municipal wastewater. Unlike natural organic matter (NOM), EfOM contains a complex mixture of residual natural organic matter, soluble microbial products, and anthropogenic organic compounds that influence advanced treatment processes, disinfection byproduct formation, membrane fouling, and contaminant transport. Although International Humic Substances Society (IHSS) reference materials have supported decades of NOM research, no standardized wastewater-derived organic matter reference currently exists, limiting comparisons among studies and the development of representative analytical methods. This study investigated the fractionation and characterization of dissolved organic matter from tertiary-treated municipal wastewater collected from an activated sludge Water Reclamation Plant (Arizona, USA) that achieves near complete denitrification. A sequential DAX-8/ DAX-4 resin isolation procedure was used to separate hydrophobic acids (HPO-A), hydrophobic neutrals (HPO-N), amphiphilic acids (AMP-A), and amphiphilic neutrals (AMP-N). Isolated fractions were characterized using CHN elemental analysis, excitation-emission matrix (EEM) fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and UV254 absorbance. The combined resin system adsorbed approximately 59% of influent dissolved organic carbon, with the DAX-8 resin removing 30–40% and the DAX-4 resin recovering an additional ~20%. Spectroscopic analyses demonstrated consistent fluorescence signatures and FTIR functional group distributions across multiple sampling campaigns, indicating reproducible isolation of major EfOM components. EEM analysis revealed distinct chemical characteristics among fractions, with acid fractions exhibiting humic- and fulvic-like fluorescence, while hydrophobic neutrals showed protein- and microbial-like signatures. CHN analysis suggested greater temporal variability within neutral fractions than acid fractions, indicating that these components may be more sensitive to changes in wastewater composition. Carbon recovery following desorption and freeze-drying remained substantially lower than adsorption efficiency, highlighting opportunities to optimize recovery protocols. The
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