Processes for enhanced NOM removal: beyond Fe and Al coagulation

Abstract

Source waters containing high concentrations of natural organic matter (NOM) have conventionally been treated using metal salts (normally Fe3 +  and Al3 +  based products). The main reason for NOM removal in potable water production is to prevent disinfection by-products (DBPs) from forming during disinfection processes. Using a common water source containing up to 15 mg L−1 dissolved organic carbon (DOC), NOM removal was assessed using 1) advanced oxidation processes (AOPs) (ultra-violet light/hydrogen peroxide (UV/H2O2) and Fenton's reagent (FR)); 2) a novel coagulant ZrCoag® (Zr4 + ); and, 3) ion-exchange (magnetic ion-exchange resin, MIEX®) combined with coagulation at reduced coagulant doses. These results were compared with optimised conventional coagulation using ferric sulphate (Fe). High levels of NOM removal were achievable, with between 7–11% increased DOC removal for the advanced treatments over coagulation with Fe3 + . The formation of DBPs (trihalomethanes) for the treatment systems were compared. There were also significant differences in the properties of the floc formed for the different treatment systems. Flocs formed after coagulation following pre-treatment with magnetic resin and coagulation using Zr4 +  resulted in significantly larger flocs compared with Fe3 +  coagulation by 37 and 27% respectively. Flocs formed using FR were smaller than Fe3 +  coagulant flocs by 28%. The paper discusses the practical implications of using the different advanced treatment processes to achieve incremental increases in overall NOM removal when compared with conventional coagulation.