Simultaneous removal of arsenic and fluoride from groundwater by coagulation-adsorption with polyaluminum chloride

The ArCIS-UNRR (R) arsenic and fluoride removal system which consists of a coagulation-adsorption process with initial pH adjustment and two filtration stages (up-flow gravel roughing filtration and rapid filtration), has been already described in previous studies. This process has been successfully implemented in full-scale plants in Argentina, with fluoride and total arsenic concentrations in raw water up to 2 mg/L and 200 mu g/L, respectively. The aim of the present study is to optimize fluoride removal when it is >2.0 mg/L. The modifications proposed were to decrease the pH level to 6.4-6.6 at the roughing filter inlet and increase the pH level to 7.2-7.6 at the rapid filter inlet to decrease residual aluminum concentration. Laboratory and pilot scale studies were performed using natural water with fluoride concentrations ranging from 2.4 to 3.2 mg/L and arsenic concentrations from 60 to 90 mu g/L. An optimal combination of operational parameters and the coagulant dose (polyaluminum chloride, PACl) was found, to achieve final concentrations of fluoride, arsenic and aluminum in treated water lower than those set by the regulations in force. Filtration run time was 10 to 12 hours; research studies are necessary to extend this period.