Continuous Water Disinfection Using Two Consecutive Catalytic Beds of CoFe2O4 and Co0.5Mn0.5Fe2O4: Mechanistic Insights into H2O2 Activation, Bacterial Inactivation, and Ecotoxicity.

Continuous hydrogen peroxide activation by heterogeneous Fenton-like catalysts offers a promising strategy for sustainable water disinfection, however the relationships between catalyst compositions, interfacial redox chemistry, reactive oxygen species generation, and long-term stability under continuous operation remain poorly understood. In particular, the effects of catalyst surface evolu tion and metal leaching on disinfection performance and treated-water safety have received little attention. Herein, we develop compositionally engineered spinel ferrite catalysts, CoFe2O4 and Co0.5Mn0.5Fe2O4, and integrate them into a sequential packed-bed reactor with progressively increasing catalytic activity for continuous-flow water disinfection. The cascade configuration combines controlled peroxide activation in the first bed with rapid oxidant decomposition in the second bed, enabling efficient bacterial inactivation while minimizing residual H2O2 in the treated water. Both catalysts were prepared as binder-free sintered granules suitable for long-term continuous operation. Electron paramagnetic resonance demonstrated that both hydroxyl radicals and singlet oxygen participated in peroxide activation, whereas Mn incorporation enhanced HO• generation through the Mn2+/Mn3+ redox cycle without changing the overall reactive oxygen species pathways. The enhanced catalytic activity shifted the dominant disinfection mechanism from adsorption-assisted surface inactivation to oxidative destruction in the bulk liquid phase. The reactor achieved stable Escherichia coli removal, maintaining bacterial concentrations below the detection limit under representative influent conditions. Ecotoxicological assessment using Daphnia magna confirmed low residual toxicity of the treated water, reflecting both minimal hydrogen peroxide residuals and limited metal leaching. Postreaction Raman spectroscopy revealed reversible surface reconstruction and active lattice participation during catalysis while preserving the integrity of the spinel framework. The proposed two-stage reactor demonstrates how catalyst composition and reactor architecture can be integrated to improve hydraulic performance, oxidant utilization, long-term catalyst stability, and treated-water safety, providing a scalable strategy for continuous advanced oxidation disinfection.