Photoelectron-Promoted Sulfate Reduction for Heavy Metal Removal without Organic Carbon Addition

Sulfate-reducing microorganisms (SRMs) show promise for heavy metal removal from contaminated environments, but their scalability is limited by reliance on organic carbon, sludge formation, and CO₂ emissions. This study investigates using photoelectrons from biogenic (Bio-ZnS) and abiogenic (Abio-ZnS) sphalerite nanoparticles to enhance the activity of <i>Desulfovibrio desulfuricans</i> G20 (G20) for sulfate reduction and lead removal without organic substrates. Both Abio-ZnS and Bio-ZnS NPs promote sulfate reduction and energy production in G20 cells under illumination without the addition of organic substrates, with Bio-ZnS achieving 1.6 times greater sulfate reduction and 3.1 times higher ATP production compared to Abio-ZnS. This superior performance of Bio-ZnS NPs is due to their wider band gap, higher photoconversion efficiency, lower charge-transfer resistance, and closer proximity to cells, which enable more efficient photoelectron uptake, enhanced intracellular electron transfer, and reduced energy consumption for motion and filamentation. The uptake of photoelectrons also promotes G20s resistance to high Pb²⁺ concentrations through enhanced PbS precipitation, biofilm formation, enzymatic detoxification, and Pb²⁺ efflux, thus improving long-term and cyclic lead removal by G20 under substrate-depleted conditions. This approach harnesses solar energy, reduces reliance on organic substrates, and lowers costs and CO₂ emissions, offering a sustainable solution for utilizing SRMs in bioremediation.