Removal of Dissolved Natural Organic Matter from Source Water with Alum Coagulation

Abstract

In this study, the effectiveness of enhanced alum coagulation for removal of natural organic matter (NOM) at various alum dosages and pH conditions was assessed for three source waters. Results from the laboratory jar tests at various conditions were compared. Tested pH ranged from 5.0 to 8.0, with alum dosages ranging from 60-120 mg l−1 for removal of dissolved NOM with various concentrations of dissolved organic carbon (DOC) and alkalinity. Alum coagulation profiles of the three source waters were also compared. For Cheng-Kung Water Treatment Plant (high DOC, high alkalinity), laboratory tests showed 50% DOC removal with alum dosage of 70 - 110 mg l−1 after acidifying the raw water to pH = 6. For Tai Lake Water Treatment Plant (high DOC, low alkalinity), laboratory tests showed that the highest DOC removal (∼50%) was achieved at an alum dosage of 80 mg l−1 at pH = 8 (natural condition). However, alum coagulation showed little DOC removal for source water from Kee-Lung River (low DOC, low alkalinity). Higher alkalinity in Cheng-Kung Reservoir accounts for the necessity to acidify the raw water before enhanced coagulation for optimum DOC removal.