Interference of the polyacrylamide coagulant in the fluorescence analysis of dissolved organic matter during water treatment

Removal of dissolved organic matter (DOM) is a major problem in drinking water treatment, because DOM modifies color, taste and odor, and carcinogenic by-products of DOM can be created during disinfection. Efficient water remediation is limited by our poor knowledge of DOM structure and properties, thus calling for advanced methods of characterisation. Here, we tested the influence of two coagulants, polymeric ferric sulfate and cationic polyacrylamide, on the three-dimensional fluorescence excitation–emission wavelength spectra of DOM during coagulation. Results of the parallel factor model reveal 3 fluorophore components C1–3. Cationic polyacrylamide decreases the linear correlation between DOM and fluorescence, e.g., from 0.92 to 0.82 for C1 and from 0.84 to 0.79 for C2. The C3 component, a protein-like material, was the most affected. Findings demonstrate the need to consider residual polymer as a potential interference when using fluorescence to assess DOM removal by coagulation.