Synergistic disinfection of multidrug-resistant bacteria using a binary rGO/electro-oxidation system: Effects on cellular activity and pleomorphism

This study evaluates the effectiveness of a binary system that combines electro-oxidation (EO) using mixed metal oxide (MMO) electrodes with different Ruthenium/Iridium ratios and a suspension of reduced graphene oxide (rGO) in a free chlorine system to inactivate S. aureus (resistant to methicillin and oxacillin) and Escherichia coli (resistant to colistin).

Electrochemical characterization by DEMS and voltammetry showed that MMO electrodes exhibit different oxygen evolution reaction (OER) potentials depending on their Ru/Ir composition, directly influencing bacterial inactivation efficiency. In NaCl, EO alone achieved complete inactivation, while in Na₂SO₄ only 40 % was achieved at 13.6 mA/cm². The addition of 0.05 mg ml⁻¹ of rGO restored bacterial inactivation to 100 %, although its efficacy declined after successive reuse cycles. Characterization by EDS, XRD, and Raman confirmed the chemical stability of rGO, whereas SEM revealed increasing particle agglomeration, which negatively impacted its performance.

The synergistic use of rGO with EO in Na₂SO₄ represents a promising alternative for water disinfection, minimizing the formation of toxic chlorinated byproducts. Evidence of the antibacterial mechanism was supported by observations of structural damage at the cellular level, including membrane rupture, increased permeability, and notable morphological deformations (pleomorphism), which reflect the loss of cell integrity due to oxidative and mechanical stress.

These findings demonstrate the potential of the EO/rGO system as a broad-spectrum and sustainable disinfection strategy for inactivating multidrug-resistant bacteria in water. Further optimization of operational parameters and nanomaterial stability is essential to enable large-scale application.