The Mobilization of Heavy Metals in River Sediment by Nitrilotriacetic Acid (NTA)

Abstract

The mobilization of heavy metals in river water and sediment by NTA during river bank filtration was investigated in the laboratory under oxygen-deficient conditions. Four PVC-columns, 1.20 m long, 0.18 m diameter, filled with river bed sediment, were percolated for 7 months with river water spiked with NTA. Water and sediment were collected from a branch of the river Rhine, where the sediment has high metal contents. The percolation rate was 10 cm. day−1. Supply water for three columns was kept oxygen-deficient. Water for the fourth column had an oxygen content of 6 mg.dm−3. To the anoxic river water NTA was added to concentrations of 0, 100 and 600 µg.dm−3 respectively. The oxic water obtained an NTA-concentration of 100 µg/l. Leachate and pore water were analysed for heavy metals, inorganic macroparameters and NTA. After percolation the sediment was analysed for bound metals. When river water and sediment contained adapted micro-organisms, NTA was degraded within two weeks in all columns. Degradation was nearly absent during the first three weeks of percolation, due to the necessary adaptation. Except for the first month, NTA was not detected in the pore water below 10-30 cm. In the first month it penetrated into the leachate. Within the concentration range considered, neither NTA- nor O2-content of the supply water affected the mobilization of the heavy metals considered.