Ferrous clay as a coagulant for arsenic reduction in groundwater

Abstract

Arsenic is present in some mechanical wells in Guatemala, posing a health risk when water is consumed at concentrations exceeding the COGUANOR NTG 29001 standard. This study evaluated the efficiency of ferrous clay as a natural coagulant for reducing arsenic in groundwater. Ferrous clay was applied at doses expressed as concentration (25 to 100 g/L) combined with sedimentation times of 30 and 60 minutes, followed by filtration of the supernatant through a controlled-porosity ceramic element. Initial and final values of pH, electrical conductivity, turbidity, color, arsenic, and total iron were analyzed. Arsenic reductions ranged from 47.37% to 80.70%, reaching a minimum concentration of 0.011 mg/L, although the regulatory limit was not achieved. All other parameters remained within acceptable ranges, and no increase in total iron was observed in the evaluated treatments. The findings suggest that ferrous clay can contribute to partial arsenic reduction under laboratory conditions and could be considered as a preliminary treatment stage. Main limitations included the lack of mineralogical/textural characterization of the material, the limited number of replicates (n=2), and the lack of operational optimization (pH and mixing); additionally, the availability of arsenic-contaminated samples was constrained by limited access to affected wells.