Effects of Energy Source Concentration on Bioleaching of Heavy Metals from Undigested Sewage Sludge by Using Iron-Oxidizing Bacterium

Abstract

The objective of the present study was to optimize the energy source addition required for bioleaching of heavy metals from undigested sewage sludge after secondary treatment. Bioleaching was conducted in a batch system with both inoculation of iron-oxidizing bacteria and the addition of FeSO4 ⋅7 H2 O in the range of 0–17.5 g L−1 . The results showed that the pH of the sludge decreased with an increase in the ferrous iron concentrations and reached the maximum acidity of pH 2.1–3.0 for treatments receiving both bacterial inoculation and substrate addition. This led to a significant solubilization of metals from the solids fraction of sewage sludge. However, solubilization behavior differed for different metal species. Solubilization of Zn was not affected by the concentration of the substrate in the range of 7.5–17.5 g L−1 , whereas solubilization of Cu and Cr was highly dependent on substrate concentration. After 10 days of bioleaching the following heavy metal solubilization efficiencies were obtained: ...