Lithotrophic Bacterial Leaching of Heavy Metals from Sediments Dredged from the Deûle Canal, France

ABSTRACT

Lithotrophic bacterial leaching of heavy metals from dredged sediments was studied in semi-pilot scale air-lift bioreactors. Prior to the bioleaching experiments, a physico-chemical characterization of the sediments comprising a sequential extraction study was conducted. The sediments turned out to be highly loaded with heavy metals, and with the exception of managanese, mainly associated to the oxidizable fraction of the sediments and thus strongly linked to the latter. The heavy metals could be classified by decreasing order of mobility as follows: Mn>Zn>Cu>Cd>Pb. The bacterial leaching was found to be strongly dependent on the nature of the mineral substrate. Sulfur gave the best solubilization results in comparison with reduced iron or with a combination of reduced iron and sulfur. In the presence of oxygen, lithotrophic bacteria oxidized sulfur into sulfates and induced an acidification of the sediments. These conditions led to the release of the metals that were tightly linked to the sediments, that is those associated with the sulfides and/or with the organic matter. With sulfur as a substrate, the solubilization percentages varied within 30 days between 72 and 93% of the total sediment content (wt/wt) for cadmium, copper, manganese and zinc. Much lower biosolubilization percentages were obtained in the case of lead because of the poor solubility of lead sulfate.