HEAVY-METAL BIOSORPTION SITES IN ASPERGILLUS-NIGER

Aspergillus niger is capable of removing heavy metals such as lead, ca dmium and copper from aqueous solutions. The role played by various fu nctional groups in the cell wall of A. niger in biosorption of lead ca dmium and copper was investigated The biomass was subjected to chemica l treatments to modify the functional groups, carboxyl, amino and phos phate, to study their role in biosorption of metal ions. The modificat ions of the functional groups which resulted from these chemical treat ments were examined with infrared spectroscopy. It was found that este rification of carboxyl and methylation of amine groups present in the cell wall of A. niger significantly decreased biosorption of the heavy metals studied. These findings suggest that carboxylate and amine gro ups are important in metal ion biosorption on A. niger biomass. Phosph ate groups and the lipids fraction of the biomass did not play a signi ficant role in biosorption of the metal ions studied. Biosorption of l ead and cadmium displaced Ca2+, Mg2+ and K+ ions present on the biomas s surface, indicating that biosorption rook place as a result of an io n-exchange process. (C) 1997 Elsevier Science Ltd.