Bioleaching technologies applied for the valorisation of dredged sediments polluted by heavy metals

The polluted dredged sediments represent a waste material whose management costs might be very high, according to pollution degree. In fact, the recent regulations do not allow that contaminated sediments are disposed of at sea and confined disposal facilities request high space that usually is not available in Italian harbours. Therefore there is a substantial need of a sustainable technology aimed at decontamination of the sediment for reuse options. The present work concerns a bioremediation study applied for harbour sediment polluted by heavy metals, sampled in the Adriatic Coast. Bioleaching of the sediment sample was performed with a mixed culture of acidophilic, chemi-autotrophic Fe/S oxidising bacteria. The effect of an anaerobic biostimulation pre-treatment on the extent of Cd, Cu, Zn, Ni, Pb, Hg, As, Cr extraction by bioleaching was evaluated. The biostimulation pre-treatment was intended to stimulate autochthonous sulfate reducing strains, to enhance the sulfide fraction in the sediment, to favour subsequent activity of reduced-sulfur-oxidizing bacteria in the subsequent bioaugmentation (bioleaching). The effect of the duration of anaerobic pre-treatment (21 and 30 days) in the presence and absence of 1% glucose was tested. The results obtained showed that the activity of the reduced-sulfur-oxidising strains was significantly enhanced after an anaerobic pre-treatment of the sediments and showed real promise for the application of bioleaching for metal polluted sediments and consequent reduction of costs for dredged sediments' management.