Novel insights into variation of dissolved organic matter during textile wastewater treatment by fluorescence excitation emission matrix

Abstract

In this work, the textile wastewater samples along two full-scale treatment trains (‘biological + oxidative’ process) were characterized by fluorescence excitation emission matrix (EEM). Four fluorescent components (C1–C4) were identified by parallel factor (PARAFAC) analysis. The polarity and apparent molecular weight (MW) of C1–C4 were investigated by high performance liquid chromatography (HPLC). By comparison of EEM spectra and HPLC chromatograms, the tyrosine-like component (C1) and the tryptophan-like components (C2 and C3) were related to Dispersant MF. Component C4 with two emission peaks suggested the formation of an intramolecular exciplex. Despite the remarkable difference of untreated textile wastewater, the polarity and apparent MW of C1–C4 as well as their variations along the treatment trains were highly similar between different wastewater treatment plants. The weights distribution of Dispersant MF among C1–C4 indicates its dominance in the protein-like fluorescence of textile wastewater. Component C1–C4 had different fate in various treatment stages. C1–C4 were poorly removed (<25%) during the anaerobic or anoxic process. A better removal efficiency of C3 (65%–80%) than C1, C2 and C4 (15%–50%) was achieved in the aerobic process. Both Fenton and chlorination process could significantly decrease the concentrations of C1–C4 (70%–100%). The concentration of C2 was strongly correlated with dissolved organic carbon (DOC), chemical oxygen demand (COD) and UV absorbance at 254 nm (UVA254). The fluorescence of C2 could be proposed as an indicator of COD and a supplement to UVA254 to evaluate treatment efficiency of textile wastewater. The results provide a better understanding of DOM variation of textile wastewater during treatment.