METAL LEACHING OF FLY-ASH FROM MUNICIPAL WASTE INCINERATION BY ASPERGILLUS-NIGER

Biological leaching of fly ash from municipal waste incineration by As pergillus niger was examined in batch cultures and compared with chemi cal leaching. A. niger grew in the presence of up to 10% (w/v) of fly ash in the medium. In the presence of fly ash A. niger produced glucon ate, whereas in its absence citrate was produced. Variation of the fly ash concentration in the growth medium (one-step process) resulted in different amounts of solubilized metals. A total of 3% (w/v) fly ash generally gave maximum extraction yields (in percent of the amount app lied). In a two-step process A. niger first was cultivated in the grow th medium, and subsequently the microbiologically produced citric acid was used as the leaching agent. At 6% (w/v) fly ash, the amounts of l eached metals (leaching for 1 day) were 81% of Cd, 66% of Zn, 57% of C u, 52% of Pb, 32% of Win, 27% of Al, and less than 10% of Cr, Fe, and Ni, respectively. Chemical leaching with commercial citric acid of equ al molarity was only slightly higher than microbial leaching. The envi ronmental quality of the residues can be improved with respect to a re -use of these materials for construction purposes.