Removal of heavy metals from MSWI fly ash using acidithiobacillus strains: Effects of substrate concentration

A mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was used to leach heavy metals from MSWI fly ash ( municipal solid waste incineration fly ash) to render them nonhazardous. Batch experiments were conducted to optimize substrate concentration for the bioleaching process. Results showed that substrate concentration significantly influenced solubilization of heavy metals and biooxidation yield of added sulfur. The optimum substrate concentration was 5 g/L. After 15 d of bioleaching, 89.7% of Cd, 81.8% of Zn, 72.6% of Cu and 29.3% of Pb were extracted from fly ash with the addition of 5 g/L elemental sulfur and bacterial inoculation. Moreover, final yield of sulfur oxidation obtained 65.2%. TCLP (Toxicity Characteristic Leaching Procedure) tests confirmed that the bioleaching process resulted in the solubility reduction of Cd, Zn, Cu and Pb to below the regulatory limits. Results also suggested metal solubilization was mainly dependent on the acidification of fly ash suspension resulted from biooxidation of added elemental sulfur.EI02129-1351