Bioleaching as a bioremediation strategy for dredged sediments polluted by heavy metals.

The present work deals with the bioremediation of a sediment sample contaminated by heavy metals, collected in the Ancona harbour, Italian Adriatic Sea, Mediterranean Sea. Bioleaching of the sediment was performed with a mixed culture of acidophilic, chemi-autotrophic Fe/S oxidising bacteria, in the presence of elemental sulphur as substrate. Such element resulted to be fundamental both for cell growth and for metal dissolution. The effect of an anaerobic biostimulation pre-treatment on the extent of Cd, Cu, Zn, Ni, Pb, Hg, As, Cr extraction by bioleaching was also evaluated: the activity of the Fe/S oxidising bacteria resulted to be significantly enhanced after an anaerobic pretreatment of the sediment. The main advantage of this two-step (anaerobic-aerobic) bioremediation approach is that microbial activity, and the consequent metal mobilisation, is independent from the availability of sulphur. These results open new perspectives for bioleaching applied as a bioremediation strategy for sediment contaminated by heavy metals.