Process optimization for silica dissolution from e-waste as a sustainable step towards bioremediation

High-purity silicon represents a major component of e-waste. Current methods for e-waste remediation are energy-intensive or chemical-based. Herein, a microbial route for silica dissolution from e-waste was explored, as microbes play an active role in balancing the silicon cycle. The study focused on an isolated silicate solubilizing bacterium (SSB) Staphylococcus gallinarum CON2 for its capability to solubilize silica in e-wafers and silicon dioxide chips. Bacterial silica dissolution was optimized for various parameters using Plackett Burman design. Heteropoly acid method was standardized for quantitative analysis of dissolved silica. Bacterial treatment of e-wafers from solar panels and laboratory-coated silicon dioxide chips were carried out under pre-optimized conditions. For comparison purpose, another SSB was also evaluated for e-waste remediation at similar conditions. The amount of released silicic acid after e-waste treatment was determined, and its presence was further confirmed by FTIR analysis. Etching and loosening of silicon dioxide particles on the surface were observed under SEM at different magnifications. The novel potential of silica dissolution from e-waste by isolated S. gallinarum CON2 was confirmed. A significant difference in the actions of both silicate solubilizing bacteria on the topography of the e-waste specimens was observed.