Optimization of metal leaching efficiency of fly ash from municipal solid waste incineration by sulfur oxidizing bacteria

Sulfur oxidizing bacteria were used to leach metals bound in municipal soli d waste incineration ny ash. Pure or mixed cultures of Thiobacilli with or without addition of anoxic sewage sludge were incubated with various amount s of fly ash for several weeks. Go-cultures with Thiobacilli and sewage slu dge grew faster than pure cultures of T. thiooxidans or cultures with only sewage sludge as inoculum. The addition of sewage sludge increased the grow th of sulfur oxidizing bacteria and simultaneously enhanced the acidificati on of the suspension. As a result, the time for fly ash processing was redu ced by 50 %. Thiobacilli were able to grow in the presence of up to 8 % (w/ v) fly ash. Depending on the amounts of fly ash added, the final pH, and th e concentration of sulfuric acid formed, different amounts of metals were l eached: over 80 % for Cd, Cu, and Zn, 60 % for Al and approx. 30 % for Fe a nd Ni (totally approx. 50 % of the heavy metals present in the fly ash) wer e extracted.