Fenton-like water disinfection using fixed-bed reactor filled with a CoFe2O4 catalyst: Mechanisms, the impact of anions, electromagnetic heating, and toxicity evaluation

Abstract

This work is a pioneering study demonstrating a promising breakthrough in water disinfection using a cobalt ferrite catalyst in a fixed bed. The performance of CoFe2O4 in E. coli inactivation is due to HO• radicals generated in the Fe3+/Fe2+ and Co3+/Co2+ redox cycles. In contrast to existing reports using cobalt ferrite nanoparticles, the bulk cobalt ferrite provides long-lasting catalytic performance in a flow reactor. The positively charged surface of cobalt ferrite attracts negatively charged E. coli membranes, which enhances disinfection. The CoFe2O4 catalyst was synthesized by the flow co-precipitation method, which allows obtaining kilogram quantities needed for industrial applications. The efficiency of E. coli inactivation was studied as a function of H2O2 concentration. For the first time, the reactor with a CoFe2O4 catalyst was additionally boosted by an electromagnetic field to decompose H2O2 and inactivate bacteria. The electromagnetically heated CoFe2O4/H2O2 system provides a significant 6 log bacterial inactivation. Importantly, cobalt ferrite is very stable under operating conditions. Only a negligible leaching of Fe and Co ions was observed. The presence of inorganic anions was beneficial for the bacterial inactivation. Ecotoxicological analysis revealed the absence of the toxicity of the treated water after using CoFe2O4/H2O2 with electromagnetic heating in the presence of bicarbonate ions. The results show that the magnetic cobalt ferrite is a promising, durable, heterogeneous catalyst for large-scale water disinfection.