Zirconium and chitosan coagulants for drinking water treatment – a pilot study

Scientists continuously search for alternative coagulants that would be able to outperform traditionally used aluminium (Al) and iron (Fe). Use of a novel metal coagulant zirconium (Zr) has been associated with enhanced organic matter reduction. On the other hand, eco-friendly non-metal solutions, such as chitosan, can provide non-toxic sludge and water with no metal residue. In fact, Zr and chitosan have been utilized in full-scale operation by several water plants in Norway providing over 50,000 recipients in small and large municipalities with drinking water. However, the use of these two agents is limited in other parts of the world. In the present work, Zr and chitosan coagulants were tested together with Al for drinking water production in both pilot and laboratory trials. All coagulants provided high quality effluents. However, the metals showed higher efficiencies in terms of reduction of humic substances, with better performance of Zr than Al. On the other hand, the amount of suspended solids in sludge produced with chitosan was 25% of the amount produced with metal salts. Chitosan also functioned over a broad pH range without affecting the pH of the treated water.