Microbial leaching of metals from digested sewage sludge in continuous system

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Abstract
Microbial leaching of metals from digested municipal sludge was studied in a continuously fed 5L capacity bioreactor using an adapted strain of Thiobacillus ferrooxidans at varying dilution rates and an inlet sludge solids concentration of 30g/l. The pH of the feed sludge was adjusted to 4.0 and leaching was conducted at a temperature of 30°C. Acceptable levels of metals in the sludge were reached with a residence time of 5 days compared to 7–12 days in the batch process. The maximum specific growth rate of 0.038/h was found for individual metals or mixture of metals involved in leaching. Ks values for Zn, Cu, and combined Zn and Cu were found to be 18.5, 43.6, and 61.3 mg/L respectively.