Practical guidelines for enhanced coagulation using UV254

Abstract

Abstract The negative effects of natural organic matter (NOM) in drinking water are well known and, where necessary, its removal is crucial. This is enforced by the increasingly stringent water regulations around the world. In South Africa, this regulation targets NOM in the form of total organic carbon (TOC), at a maximum of 10 mg/L. Enhanced coagulation (EC), a multiple objective chemical dosing strategy, offers a viable method of NOM removal, and this study explored its use for typical South African raw waters. A consistent and reproducible jar test procedure was developed and applied to 19 widely different raw water samples collected from different locations and at different times of a year long period. These samples consisted of a wide range of alkalinity, UV254 and turbidity values. Three criteria were developed and applied to determine the best EC dosage for the optimal removal of UV254 without compromising residual dissolved organic carbon (DOC) and turbidity. DOC was measured, prior to and after batch tests, to confirm removal similarities with UV254 and compliance with national standards. The resultant percentage removals of UV254 and DOC ranged between 56 to 96 % and 45 to 94 % respectively, irrespective of water source, period and coagulation dosage. The settled water residual turbidity values were less than 1.5 NTU. The costs for EC were found to be comparable to those for conventional coagulation in all cases