ABSTRACT
ABSTRACT: Elevated concentrations of arsenic (As) along with iron (Fe) often occur in the ground waters in flood plains of West Bengal (India) and Bangladesh. In practice As can be removed when Fe is added as coagulant after oxidation of As(III) to As(V) and adsorbing As(V) onto Fe hydroxides. In Bangladesh iron removal units (IRU) were installed to remove naturally occurring Fe to supply Fe-free water to villagers. Hence investigations were carried out to examine the efficiency of IRU for As removal and to study whether similar As removals can be obtained by simple sedimentation in buckets compared to the IRU. The results show that IRUs have removal rates for As comparable to simple sedimentation. It was observed that Fe/As molar ratios above 80 were necessary to achieve residual As concentrations below 50g/L. Based on the extensive data available on As and naturally occurring Fe concentrations in wells, removal of As may be attained at a quarter of the tube wells exceeding an As concentration of 50g/L. The results further showed that due to improper construction of the IRUs, untreated water was mixed with treated water and hence resulted in poorer Fe and As removals. It is concluded that removal of As by naturally occurring Fe in IRUs in the areas with elevated Fe concentrations is functioning and can be employed as an As removal method, but further research is needed to improve the construction of the IRUs with a possibility of introducing a simple As(III) oxidation unit and to improve the Fe removal capacity of the IRU and thereby increase the As removal efficiency.
