Water Research 38 (2004) 3205–3214 Bioleaching of heavy metals from contaminated sediment by indigenous sulfur-oxidizing bacteria in an air-lift bioreactor: effects of sulfur concentration Shen-Yi Chen, Jih-Gaw Lin* Institute of Environmental Engineering, National Chiao Tung University, 75 Po-Ai Street, Hsinchu, Taiwan Received 18 July 2003; received in revised form 16 April 2004; accepted 30 April 2004 Abstract The effects of sulfur concentration on the bioleaching of heavy metals from the sediment by indigenous sulfur- oxidizing bacteria were investigated in an air-lift reactor. Increasing the sulfur concentration from 0.5 to 5g/l enhanced the rates of pH reduction, sulfate production and metal solubilization. A Michaelis–Menten type equation was used to explain the relationships between sulfur concentration, sulfate production and metal solubilization in the bioleaching process. After 8 days of bioleaching, 97–99% of Cu, 96–98% of Zn, 62–68% of Mn, 73–87% of Ni and 31–50% of Pb were solubilized from the sediment, respectively. The efficiency of metal solubilization was found to be related to the speciation of metal in the sediment. From economical consideration, the recommended sulfur dosage for the bioleaching of metals from the sediment is 3 g/l. r 2004 Elsevier Ltd. All rights reserved. Keywords: Bioleaching; Indigenous; Sediment; Heavy metal; Sulfur concentration; Thiobacilli species 1. Introduction Sediment is the ultimate fate for natural and anthro- pogenic pollutants in the aquatic environment. Sediment is generally highly contaminated with various types of pollutants in the countries of dense industrialization. For a successful remediation, dredging of contaminated sediment is one of important alternatives besides controlling the pollutants at sources and building sewer systems. Most of the sediment dredged from contami- nated aquatic bodies such as river and lake contains high concentration of toxic pollutants such as heavy metals (Fo¨rstner and Calmano, 1998). Because of stringent disposal standards, this metal-contaminated sediment cannot be disposed off on lands without proper treatment. Environmental engineers and managers are facing new challenges regarding the management and treatment of a large quantity of contaminated sediment. From this perspective, development of a suitable and a cost-effective technology for removal of heavy metals from the contaminated sediment is needed. Conventionally, physical or chemical technologies are used for treatment of metal-contaminated sediments. However, these technologies often have some limitations in practical application (Rulkens et al., 1995). The microbial method is an efficient and cost-effective alternative to chemical and physical methods of remediating many environmental pollution problems because of its low demand for energy, material and less generation of waste byproduct (Hsu and Harrison, 1995). Bioleaching is one of the microbial methods lately considered highly promising for the treatment of metal- containing or metal-contaminated solids, e.g. ores, sludges, soils, swine manure and sediments (Blais et al., ARTICLE IN PRESS *Corresponding author. Tel.: +886-3-5725958; fax: +886-3- 5722681. E-mail address: jglin@mail.nctu.edu.tw (J.-G. Lin). 0043-1354/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.04.050