Experimental evaluation of cationic polyelectrolytes for removing natural organic matter from water

The effectiveness of water treatment processes in removing natural organic matter varies with the nature of the natural organic matter (NOM), its mole cular size, polarity and charge density, and with properties of the raw wat er such as turbidity and hardness. In some cases conventional alum treatmen t is inefficient. We have compared NOM removals achieved by conventional an d polymer-based processes in bench-scale treatment of reconstituted ground and surface waters of varying colour, made from NOM isolated from the same waters. NOM isolates were fractionated by adsorption on non-functionalised resins and an anion exchanger, and characterised by size exclusion chromato graphy. Jar tests with the isolated NOM compared coagulation with polyelect rolytes, alum clays and metal oxides, with each of the inorganics being in conjunction with a polyelectrolyte. Jar tests on reconstituted waters with alum and/or cationic polyelectrolyte show synergistic benefits from combinations of the two. The more hydrophob ic NOM fractions were the most easily removed by polymer. The performance o f cationic polymers improved significantly with increasing charge density a nd molecular weight. An alum/polymer combination is the most attractive tre atment option. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.