Similarities in effluent organic matter characteristics from Connecticut wastewater treatment plants

Effluent organic matter (EfOM) from five Connecticut (USA) municipal wastewater treatment plants was isolated with DAX8 (hydrophobic fraction) and XAD4 (transphilic fraction) resins. Isolate recoveries ranged from 18 to 42% of the total organic carbon for DAX8 resin and from 6 to 12% for XAD4 resin. Isolated EfOM was characterized by traditional organic geochemistry techniques. Weight-averaged molecular weights of extracted EfOM by size exclusion chromatography were 450-670 Da with higher weights observed for the hydrophobic fractions than the transphilic fractions. Fluorescence characterization showed both humic- and fulvic-like fluorescence, as well as tryptophan- and tyrosine-like fluorescence, the latter not commonly observed for terrestrial organic matter. Fluorescence indices were between 1.5 and 1.9 with lower values observed for hydrophobic EfOM fractions than for transphilic fractions. Specific ultraviolet absorbance was measured between 0.8 and 3.0 L mg⁻¹ m⁻¹ with higher values for the hydrophobic EfOM fractions. Together these results indicated that isolated EfOM is similar in characteristics to microbially derived organic matter from natural aquatic systems. Little variation in EfOM characteristics was observed between the five wastewater treatment plants, suggesting that the characteristics of EfOM are similar, regardless of treatment plant design.