Impact of reactive oxygen species on cell activity and structural integrity of Gram-positive and Gram-negative bacteria in electrochemical disinfection system

High efficiency, eco-friendly, and without disinfection byproducts rendered the hydroxyl radical-dominated electrochemical process a promising disinfection technology. Inconsistent disinfection performances have been reported for Gram-positive (G+) and Gram-negative (G−) bacteria in *OH-dominated disinfection system. To thoroughly present and elucidate the different responses of G+ and G−, Fe-Co/CA cathode and Ru-Ir/Ti anode was fabricated. Under 22.73 mA/cm2, E. coli were completely inactivated within 45 min, while there were about 2 logs of S. aureus were inactivated. Moreover, the sublethal injury of E. coli outperformed that of S. aureus as well. However, when E. coli and S. aureus coexisted, the disinfection efficiencies were inhibited for both E. coli and S. aureus. The subcellular damage of E. coli and S. aureus were different as well. With the reaction, cell surface hydrophobicity for both E. coli and S. aureus increased. However, E. coli obtained increased negative zeta potential after treatment, which promoted the development of electrochemical disinfection, while S. aureus obtained decreased negative zeta potential which resulted in significant agglomeration. The determination of malondialdehyde (MDA), phosphate concentration, and the leakage of Lactate dehydrogenase (LDH), as well as the degradation of protein, TOC, and nucleic acid, and SEM observation, illustrated the cell well and cell outer membrane were the first barrier to OH-dominated disinfection. The thick and rigid cell wall and the stable structure of peptidoglycan (PGN) in S. aureus cells contributed to the high resistance of S. aureus.