13. Bioleaching of Selected Metals from E-Waste Using Pure and Mixed Cultures of Aspergillus Species

Printed circuit board (PCB) is an essential part present in electronic waste (e-waste). Rich metallic content including base, precious, and toxic metals makes PCB a secondary metal reservoir. Recycling of PCB is necessary to conserve natural resources and to protect the environment. Bioleaching process is preferred over the conventional metallurgical techniques for metal recycling from e-waste due to its better efficiency and environmental compatibility. Metal bioleaching from e-waste employing heterotrophic microorganisms like fungi is the comparatively less explored area. In this context, bioleaching of selected metals such as Cu, Ni, and Zn from e-waste in the form of desktop PCB using pure and mixed cultures of Aspergillus species was attempted. Aspergillus niger was chosen for its organic acid production ability to presumably help in bioleaching of metals. As the metals are usually embedded in the polymer matrix in the PCB, Aspergillus tubingensis was selected for its polymer-degrading ability. The bioleaching experiments were performed using pulverized waste PCB (WPCB) in the particle size range of 0.038–1 mm for a period of 33 days at 1 g/L of pulp density. Results showed that the pure culture of Aspergillus niger was able to leach a maximum of 71% Cu, 32% Ni, and 79% Zn. Similarly, the corresponding maximum metal leaching efficiency employing a pure culture of Aspergillus tubingensis was 54% Cu, 41% Zn, and 14% Ni. Using mixed cultures of Aspergillus species, there was a marginal increase in metal bioleaching for Cu and Ni with extraction efficiency of 76 and 36%, respectively. Extraction efficiency of 63% for Zn was observed using the mixed culture. Results indicated the practical feasibility of fungal bioleaching using pure and mixed cultures of Aspergillus species for metal recycling from e-waste for prospective beneficiation.