Effect of Oxygen Supply on Bioleaching Sediments Contaminated by Heavy Metals

摘要

A bioremediation process for sediments contaminated by heavy metals (Me) has been developed and tested on a pilot scale. In the core stage, solid-bed bioleaching of sediment using elemental sulfur (S°) as leaching agent is performed. Controlled S° oxidation is an essential task for optimizing the bioleaching process. The effect of oxygen supply on acidification, S° oxidation and Me solubilization and sulfur related yield coefficients was studied in a suspension reactor and a lab-scale percolator system. Variation of oxygen supply was realized by controlling the gas flow and oxygen concentration in the aeration gas. Oxygen consumption rates during suspension leaching were not affected until the dissolved oxygen concentration was reduced below 0.05 mg/L. The growth of S° oxidizing autotrophic bacteria was stoichiometrically balanced resulting in Y_(O_2/S) of 1.21 g/g. The oxygen supply varied between 150 and 0.5 mol_(O_2)/mol_(S°) over 28 d of solid-bed leaching. Maximum Me solubilization was reached already at an oxygen supply of 7.5 mol_(O_2)/mol_(S°). Lowering to 0.5 mol_(O_2)/mol_(S°) resulted in retarding acidification and Me solubilization. Both the microbial S° oxidation and Me solubilization were correlated with the oxygen supply, revealing that control of the aeration regime offers a suitable means for optimizing solid-bed leaching performance.