Removal of arsenic and fluoride from drinking water with cake alum and a polymeric anionic flocculent

The combined use of cake alum and a polymeric anionic flocculent (PAF) for removal of arsenic (As) and fluoride (F) from drinking water has been evaluated in water from two wells at Meoqui City, Chihuahua, Mexico. Field data revealed that As and F concentrations may, by this method, be reduced up to 99% and 77%, respectively. The addition of small amounts of PAF greatly facilitated sedimentation of the precipitate. Sodium hydroxide (8% NaOH solution) was used to adjust the pH near to an optimal 7.1. The efficiency of F removal depended on the amount of cake alum employed and varied with pH, whereas As removal required only the presence of cake alum. Adsorption of inorganic contaminants, which helps precipitation of metal hydroxide solids, was likely to be the dominant mechanism for F and As removal.