Enhanced Coagulation Using Al/Fe(III) Coagulants: Effect of Coagulant Chemistry on the Removal of Colour-Causing NOM

The addition of excess coagulant and lowering the coagulation pH in order to improve the removal of NOM and DBP precursors have been defined as ‘enhanced coagulation’. However, as a consequence, sludge production and treatment costs are increased, and the chemical storage and feed facilities need to be changed. Through developments in coagulant chemistry, various types of pre-polymerised coagulants have been prepared in recent years and been applied widely. In comparison to conventional coagulants under such ‘enhanced coagulation’ conditions, pre-polymerised coagulants can improve NOM and THMFP removals at relatively lower dosages. In addition, this results in a reduction in the sludge production and treatment costs, and the existing facilities in a water treatment works need not be changed by the use of pre-polymerised coagulants.