Effectiveness in chlorite removal by two activated carbons under different working conditions: a laboratory study

Activated carbon is used in many drinking water facilities because it can remove a broad spectrum of contaminants (e.g., herbicides, pesticides, heavy metals, etc.) or to replace anthracite coal in dual media filters. In recent years, liquid chlorine has been substituted by chlorine dioxide (ClO2) because, for instance, it can remove natural organic matter in raw water without formation of harmful disinfection by-products. Interest in chlorine dioxide is due to formation of chlorite (ClO2-), which can be potentially toxic for humans. In this study, the authors investigated the applicability of two activated carbons coming from different matrices (coconuts and bituminous) as technology for chlorite removal. The activated carbons were tested at different conditions (virgin and pre-loaded with some substances) in order to simulate full-scale working situations, and their Freundlich isotherms were determined. The results show a good affinity of virgin carbons in chlorite removal (about 80%), but the pre-loading significantly affected the efficiency of the chlorite removal process, reducing it to only 19%. An investigation into the main removal mechanism used by the carbons for chlorite removal was also done. Results show that activated carbons used both reduction and adsorption processes.