In this work, coagulation features and characteristics of dissolved organic matter (DOM) in combined sewer overflow (CSO)
wastewater were investigated. Ferric chloride (FeCl3) and polyaluminum chloride (PAC) were employed in the coagulation
process. Results showed that both FeCl3 and PAC are effective in removing turbidity and total phosphorus (TP). Removal
efficiencies were all above 90% when dosages were reasonable. Chemical oxygen demand (COD) removal efficiency was
between 60% and 70%. The removal efficiency of ammonia nitrogen (NH4+-N) and total nitrogen (TN) was 10%–20% only.
Comparisons of the removal efficiency for COD, turbidity, NH4+-N, TN, and TP in different concentrations of raw wastewater
with the same dosages of FeCl3 and PAC were also investigated. Results showed that water quality of raw wastewater is one of
the influential parameters for the optimized treatment of CSO wastewater. The molecular weight (MW) distribution of DOM in
the initial and the coagulated samples was determined by gel filtration chromatography (GFC) and ultrafiltration technology.
Compared with the initial wastewater, coagulated samples had much narrower distributions of MW. DOM fraction that MW>
30kDa, especially fractions that MW> 100kDa, can be removed effectively by coagulation using FeCl3 and PAC.