Bio-mobilization of Heavy Metals from Contaminated Sediments by Acidophilic Microbial Consortia

This work deals with bioremediation of dredged sediments contaminated by heavy metals. Consortia of acidophilic bacteria were added to sediments collected from the Ancona harbor (Adriatic Sea) in order to test their ability to remove heavy metals and thus to obtain valuable material suitable for different purposes (e.g. building industries or beaches nourishment). The efficiency of different bacterial consortia was compared. The simultaneous addition of autotrophic Fe/S oxidizing bacteria and heterotrophic Fe reducing bacteria to the sediment provided the highest heavy metal removal (>90% for Cu, Cd, Hg and Zn). These findings lead to hypothesize that the two metabolically different microorganisms, cooperating through a mutual substrate supply, can enhance their performance in the removal of heavy metals from the sediment. Mobilization yields in treatments based either on Fe/S oxidizing strains or on Fe reducing bacteria were similar: heavy metal extraction yields typically ranged from 40% to 50%. The additional advantage of the new bioaugmentation approach proposed here is that it is independent from the availability of sulfur. These results open new perspectives for the bioremediation technology for the removal of heavy metals from highly contaminated sediments.