Optimization of operation condition of water treatment system based on the in-situ observation of the reaction of arsenic, iron and manganese

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During the first year of the project, the principal goal was the development of the procedure to obtain XAFS spectrum at the solid - liquid interface of the biological filter where oxidation of dissolved Mn(II) to Mn(III) or Mn(IV), and accumulation of the manganese oxides are taking place. This was achieved by boring a window (fitted with polyimide film) on the empty plastic column, packing the column with biological filter acclimated for Mn removal, and applying the quick XAFS measurement technique. In-situ measurement of manganese oxidation was possible when water containing 4 mg/L of Mn(II) was fed to the column. Likewise, an attempt was made to observe the removal of As(III) (arsenite,) at the solid - liquid interface of the biological filter when raw water containing Fe(II) and As(III) was treated. A house-made column that can resist the pressure build- up due to accumulation of iron hydroxides on the filter was used to obtain As K-edge spectra when water containing 8 mg/L or 40 mg/L of Fe and 4 mg/L of As was fed to the biological filter. The results suggested that As(3) was sorbed on the biologically formed iron oxides as As(3), and was gradually oxidized to As(5).