Arsenic Removal from Ground Water by Sand Filtration during Biological Iron Oxidation

Abstract

Arsenic removal from ground water by iron oxidizer (Leptothrix spp) was investigated in this study. Batch and column studies were conducted with initial 500 µg/l and 5 mg/l of arsenic and iron, respectively. Batch results showed that 60 % and 51 % As(III) was removed during biological and physicochemical Fe(II) oxidation respectively whereas 96 % As(V) was removed in both cases. On the other hand, 50 % removal of As(V) was observed by adsorption on the iron hydroxides that had been produced after 24 hrs mixing, while As(III) was not adsorbed. It seemed that As(III) were oxidized during biological Fe(II) oxidation and iron oxidizing bacteria itself didn't oxidize As(III) to As(V). Overall As(III) removal efficiency was investigated in a biological sand bed column. Residual arsenic concentrations in the column effluent were always less than 50 µg/l at the flow rate of 7.2 and 3.6 l/d. Phosphorus was also removed very effectively. The sludge analysis showed that the biological iron and arsenic oxidation and their subsequent adsorption were taken place mainly at the top of the column bed. This cost effective technology could be applied to treatment of heavily arsenic and iron contaminated ground water.