NOM removal: evaluating five process alternatives to alum coagulation

Bench-scale experiments were conducted to evaluate disinfection by-product (DBP) precursor removal by coagulation with alum and ferric sulfate (FS), intermediate ozonation (IO3), powdered-activated carbon (PAC), ion exchange resin (IX), and spiral-wound nanofiltration (NF). The effect of source water quality on process performance was also assessed on six source waters. Overall, NF offered the best performance in terms of dissolved organic carbon (DOC) removals along with lower DBP concentrations in every tested condition except for DOC-rich waters (13-15 mg/L). Conventional treatment coupled with recirculated PAC adsorption (Actiflo (R) Carb) was the process configuration providing the most consistently low DOC (less than 2 mg/L), facilitating DBP regulation compliance. IX/alum and alum/IO3 reduced DBP concentration to a lesser extent, but proved to be more efficient than conventional treatment with alum alone. In terms of effluent DBP concentration, FS outperformed alum at higher coagulant dosages, whereas alum offered a superior performance at lower dosages. Finally, this investigation shows the relevance of conducting treatability assays to identify the most suitable treatment alternative for DBP control.