Arsenic removal by oxidation of iron hydroxide and settlement of co-precipitation into gravel spaces

We have analyzed the water of all tubewells used for drinking in Santa village in the Jessor district, Bangladesh since 1997. The following fact has been confirmed from the survey. The tubewells with arsenic concentrations exceeding the limit in Bangladesh(0.05 mg/l) were approximately 90%. High contamination of arsenic was found in the south pail of the village and arsenic concentration tended to decrease towards the north. The distribution of ferrous ion concentration is in accordance with that of arsenic contamination. The pentavalent arsenic concentration in groundwater was higher than that of trivalent in the north of Santa, but in the south trivalent arsenic concentration was higher than that of pentavalent. it seemed that the groundwater was in oxidation state in the north part of the village but in south it was in reduced state. Arsenic elution to the groundwater is mainly caused via the reduced state in the groundwater: iron oxyhydroxide (FeO.OH), which trapp the arsenic in the groundwater, changes to iron hydroxide (Fe(OH)(2)) in reduced state. men the arsenic is became free and released in the groundwater. By applying the above arsenic elution mechanism, we developed the arsenic removal experiment, namely by oxidizing iron hydroxide and trivalent arsenic in the groundwater and settling co-precipitation of iron oxyhydroxide and pentavalent arsenic between the gravels of the HRF( horizontal roughing filter).