Defluoridation of groundwater by a hybrid process combining adsorption and Donnan dialysis

Abstract

According to World Health Organization norms, the upper limit of fluoride concentration in drinking water was 1.5 mg 1 −1. The purpose of this study is to apply a hybrid process that combines the adsorption on conventional solid adsorbents such as aluminum and zirconium oxide along with a specific Donnan dialysis (DD) procedure to treat groundwater with an excessive fluoride concentration of 4 mg 1 −1 resulting from phosphate mining in Morocco. The DD pre-industrial pilot was equipped with ACS anion-exchange membranes (Tokuyama Co.) having a total area of 0.176 m 2. The DD process was studied under two circulating modes of the receiver solution, single pass and batch, whereas the feed solution flowed continuously as a single pass. To maintain the fluoride concentration below the acceptable values at the outlet of the feed compartment, the extracted fluoride ions are adsorbed by Al 2O 3 and ZrO 2, which were added in the receiver solution. The mineralization of the treated groundwater was not modified. The cation composition remained unchanged, whereas anions, except chloride, were partially eliminated and substituted by chloride ions, giving a fluoride concentration below the acceptable values.