Fluorescence analysis of a standard fulvic acid and tertiary treated wastewater

Fluorescence measurements (emission scan, synchronous scan, and excitation-emission matrix [EEM] scan) were used to compare characteristics of two sources of dissolved organic carbon (DOC) from distinctly different origins: (i) a standard fulvic acid from the Suwannee River (SRF sample) and (ii) an unfractionated DOC sample from a tertiary wastewater treatment plant (MWW sample). Two methods were demonstrated that quantitatively differentiated allochthonous DOC (e.g., SRF) from autochthonous DOC (e.g., MWW). The MWW sample exhibited fluorescence peaks undetected in the SRF sample, at shorter wavelength pairs (e.g., 220 nm:300 to 350 nm) than the dominant peaks in the SRF sample (e.g., 220 nm:450 nm). These peaks may be associated with base or neutral fractions, potentially enriched in organic nitrogen. Effects of DOC concentration and solution pH were discussed. A simple procedure was recommended (pH = 3; DOC = 1 mg/L; dilution with 0.01 M KCl) that minimizes the need to correct spectra for inner-filter absorbance effects. A method, using synchronous fluorescence, to estimate the percentage of DOC from different sources when mixed together was also presented. Further work to understand the structural properties of DOC that fluoresce in wastewater samples, especially at shorter EEM wavelength pairs, will enable water managers to better understand the influence of wastewater on DOC in receiving waters (e.g., rivers, lakes).