Development for Arsenic Removal using Iron Reducing Bacteria in Ground Water

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Experiments for IRB method to remove iron, manganese, arsenic and ammonia started at the water purification plant in Muko city, Kyoto and earth work site for flood control in Kawanishi city, Hyogo in 2006. Arsenic concentrations of both site are 19.3 mg/L in Muko city and 218 mg/Lin Kawanishi city. The experiment in Muko city was implemented with different percolation velocities as 150m/day to 600 m/day, and the result was around 72 to 98% removals of iron, manganese and arsenic. The experiment in Kawanishi city was implemented with 500m/day percolation velocity, and the result was 75% removal of iron, 59% removal of arsenic, however manganese removal was not stable. According to XAFS analysis at the Spring-8, As(III) and As(III) which was oxidized as As(V) was sorbed near IRB at first, and sorbed As(III) was gradually oxidized to As(V). It means that this result disproves accepted notion (arsenic was sorbed after oxidation.).The experiment in Muko city was continued as first stage and second stage in 2007. Iron removals of both stage were more than 90% and stable. Arsenic removal was around 60% in second stage better than first stage. Manganese was not removed in both stages. Ammonia nitrification in second stage was better than first stage. It seems that differences of filter media and back-washing frequency. Small column tests implemented in second stage got a result removal of manganese and nitrification of ammonia after 50 days. XAFS analysis found living IRB aggregation was the highest sorption of As(V). And As(III) sorption and its velocity of living IRB aggregation was better than As(V) sorption and its velocity of freeze-dried IRB aggregation.