Removal of chlorite from drinking water: laboratory and pilot-scale studies to predict activated carbon performance at full scale

Chlorite is a by-product that can be produced in the disinfection process of a drinking water treatment plant (DWTP) using chlorine dioxide. The aim of this work was to evaluate the influence of the adsorption process with activated carbon on chlorite removal and to demonstrate how laboratory-scale and pilot-scale tests can be useful to predict granular activated carbon (GAC) performance on chlorite removal at full scale in a DWTP. A first series of tests were carried out at laboratory scale using small carbon columns. A second series of tests were performed at semi-full scale using a pilot plant at the DWTP of Vescovana (Padova, Italy). The laboratory-scale tests show that carbon pre-loading significantly reduces the ClO2-removal yield, by about 30%-40%. Both laboratory-scale tests and small column tests show that in virgin conditions the mineral carbon shows a higher ClO2-removal efficiency than the vegetal one, while in pre-loaded conditions an opposite behavior is observed. The results of the pilot plant test show that GAC ensures a good ClO2-removal yield, close to 55%. The results show that small column tests at laboratory scale are extremely useful to predict pilot column performance and, therefore, full-scale DWTP performance.