Effect of enhanced coagulation on the characteristics of dissolved organic matter in secondary treated effluents

The effect of enhanced coagulation on the chlorination activity and fluorescence characteristics of dissolved organic matter (DOM) in the secondary treated effluent from the B wastewater treatment plant (Shenyang) was investigated. FeCl₃·6H₂O was used as a coagulant in this study. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The results showed that a DOC removal of 55.3% was obtained under the enhanced coagulations (coagulant dosage 80 mg·L^-1, pH=5.00). The removal of HPO-A by enhanced coagulation was the highest while that of HPI was the lowest. HPO-N increased in specific trihalomethane formation potential (STHMFP), where the other four DOM fractions decreased in STHMFP, as a result of enhanced coagulation. Enhanced coagulation could effectively remove fulvic acid-like fluorescent materials and the polycyclic aromatic fluorescent materials with more aromatic rings and a higher degree of conjugation. The correlation between DOC removal and fluorescence intensity reduction of DOM fractions resulted from enhanced coagulation was not significant.