Insights into Bacterial–Viral Interactions during Electrochemical Disinfection with ZnO Nanoflower-Decorated Laser-Induced Graphene Electrodes

The widespread occurrence of pathogens in wastewater necessitates broad-spectrum disinfection strategies, and electrochemical disinfection has emerged as a promising treatment option. However, its disinfection potential against mixed pathogen systems that closely mimic real-water conditions remains scarce. Laser-induced graphene (LIG) provides a scalable, chemical-free, and one-step approach for synthesizing graphene, making it suitable for microbial electrochemical inactivation. The performance of LIG can be enhanced by incorporating metallic dopants. Although ZnO-LIG and other LIG–metal composites have been studied for their electrochemical properties, the combined advantage of high-surface-area ZnO nanoflowers (ZnNf) integrated with the conductive LIG network for disinfecting mixed bacterial and viral contaminants has not been explored. This work addresses that gap by synthesizing ZnNf-LIG composite electrodes for the electrochemical disinfection of mixed pathogens. Optimization studies revealed that a 5% ZnNf loading on LIG exhibits the highest electrochemical activity and disinfection performance, outperforming pristine LIG, as well as 1 and 10% ZnNf-LIG. Using these electrodes, Staphylococcus epidermidis and Escherichia coli were completely inactivated within 4 h in single systems, while mixed bacteria required 6 h. For viruses, single systems achieved ∼5.1, ∼2.0, and ∼1.0 log reductions for bacteriophages MS2, Phi6, and T4, respectively, but decreased to ∼2.5, ∼1.25, and ∼0.8 logs in mixed systems. Correspondingly, disinfection rate constants declined from 1.59, 0.84, and 0.39 h–1 in single systems to 0.98, 0.47, and 0.26 h–1 in mixed systems, respectively. Notably, MS2 showed ∼1.5 times lower log reduction in the mixed system. Scavenging experiments confirmed the prominence of the reactive species-driven disinfection mechanism in batch mode, as MS2 inactivation reduced from ∼5.1 to ∼0.6 logs with scavenger addition. Thus, these findings highlight the role of competitive interactions and shielding among coexisting pathogens toward disinfectants in reducing disinfection efficiency and demonstrate the promise of ZnNf-LIG electrodes for advanced, realistic water treatment applications.