Reduction of dissolved organic matter in secondary municipal effluents by enhanced coagulation

Jar test experiments were performed to investigate the reductions of dissolved organic matter (DOM) in secondary municipal effluents by coagulation, as well as the effect of coagulation on the structural and functional properties of DOM fractions. The reductions of 9-58% and 17-71% in dissolved organic carbon (DOC) and the removals of 30-75% and 30-83% in absorbance of ultraviolet light at 254 nm (UV-254) were obtained by coagulation of two secondary municipal effluents, respectively. Moreover, the order of DOC and UV-254 removals by coagulation was pH 5 > pH 6 > unadjusted pH at all coagulant dosages. The reductions of the bulk fluorescent materials by coagulation were lower than those of UV-254 absorbing compounds. Among four types of fluorophores, aromatic protein-like fluorophores were preferentially removed by coagulation. The coagulation treatability of hydrophobic acid (HPO-A) was the highest and that of hydrophilic fraction (HPI) was the lowest, among five DOM fractions. In addition, the value of specific ultraviolet light absorbance for each DOM fraction decreased significantly after coagulation. The Fourier-transform infrared spectra revealed that aromatics were effectively removed by coagulation while coagulation seemed to be inefficient in removing amide-2 functional groups and those hydrocarbons exhibiting absorbance characters at 2950-2850 cm^-1.