BIOLEACHING OF HEAVY-METALS FROM CONTAMINATED AQUATIC SEDIMENTS USINGINDIGENOUS SULFUR-OXIDIZING BACTERIA - A FEASIBILITY STUDY

The removal of heavy metals from contaminated river sediments was stud ied using suspension leaching under laboratory conditions and percolat ion leaching in a pilot plant. The leaching potential of indigenous su lfur-oxidizing bacteria was compared with acid treatment. Bioleaching with elemental sulfur as substrate was found to be better than treatme nt with sulfuric acid for the solubilization of all metals tested. The physical and chemical properties of the sediments used in this study did not affect leaching capacity under optimum conditions in the labor atory. Under the practical conditions in the pilot plant, the redox st ate of sludge had a considerable influence on leaching efficiency. In a deposited oxic sediment with good permeability, about 62% of the met als tested were removed by percolation leaching after 120 days. Zn, Cd , Ni, Co and Mn were sufficiently leached to enable treated sediments to be reused as soil. In a freshly dredged anoxic sediment, only a tot al of 9 % of metals were removed. The results indicate that freshly dr edged sediments need to undergo pretreatment before percolation leachi ng to improve mass transfer and to activate the leaching active bacter ia. (C) 1998 IAWQ. Published by Elsevier Science Ltd.