Electrocatalytic disinfection of E. coli using Ni-Fe/Fe3O4 nanocomposite cathode: Effect of Fe3O4 nanoparticle, humic acid, and nitrate

Abstract

The present study aimed to propose an effective system for Escherichia coli (E. coli) disinfection as a model of pathogen bacteria via an electrocatalytic system using Ni-Fe/Fe3O4 nanocomposite cathode in the absence and presence of nitrate (NO3–) by enhancing the inactivation of bacteria using Fe3O4 NPs and humic acid (HA). The non-precious Ni-Fe electrode was synthesized through an electrodeposition method. The fabricated nanocomposite electrode was characterized by Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (FESEM/EDX) and X-ray Photoelectron Spectroscopy (XPS).The experiments were performed in the pH of 6.5, 10 mM sodium chloride (NaCl), 50 mg/l NO3–, 105 CFU/mL E. coli, 20 mg/l HA, and the current density of 4 mA/cm2. The proposed electrocatalytic system was reached to complete E. coli inactivation in 12 min with energy consumption of 0.111 KWh/m3. The time of complete disinfection was increased up to 120 min after providing NO3– in the system due to the reaction of chlorine (Cl2) compounds with some by-products of NO3– reduction, such as nitrite (NO2–) and ammonium (NH4+). Moreover, the NO3– reduction was achieved 72.8% in 120 min. The complete inactivation of E. coli was achieved in 60 min using HA, due to the production of hydroxyl radical (·OH). The utilizing of HA had no effect on the NO3– reduction. Therefore, the HA presents an enhancer effect for disinfection. The obtained results revealed that the electrocatalytic performance of Ni-Fe/Fe3O4 had a superb capability for water disinfection and NO3– reduction separately and simultaneously since it was endowed with effective mechanisms in the production of active disinfectant species, such as ·OH, chlorine dioxide (ClO2), and hydrogen peroxide (H2O2).