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.