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[Influence of fly ash concentrations on the growth of Aspergillus niger and the bioleaching efficiency of heavy metals].

The bioleaching of municipal solid waste incinerator (MSWI) fly ash for metals extraction by Aspergillus niger was investigated. The influence of fly ash concentrations on the biomass concentration, the pH of suspension, the kinds of bio-produced organic acids and the metals extraction yield during the bioleaching process were studied and the leaching toxicities of fly ash before and after bioleaching were compared. The results showed that the decrease of pH was due to generated organic acids by Aspergillus niger during bioleaching, which resulted in the metals extraction from the fly ash. The alkaline and the heavy metals toxicities of fly ash inhibited the Aspergillus niger growth, which was shown as the "lag phase". When fly ash concentration was 20 g/L, the maximum biomass was 28.61 g/L (after bioleaching 192 h), and the minimum pH was 3.85 (after finished bioleaching). The bioleaching efficiency was the highest (i.e., 93.06% for Cd, around 70% for Mn, Pb and Zn, 22%, 33% and 47% for Fe, Cr and Cu, respectively). The TCLP results of the fly ash after bioleaching indicated that the leaching toxicities of the treated fly ash were far lower than the regulated levels of China.