A multi-phase reactions for organic carbon removal in bio-electrochemical reactors employing Fe2O3-synthesized nanoparticles

Two Poly(methyl methacrylate) reactors were fabricated, and the flow of synthetic Dissolved Organic Carbon (DOC) was maintained. Humic acid was used as the source of organic carbon, with a water pH of 7-8.5, TDS of 220-240 mg/L, and EC of 0.4-0.5 mS/cm. Iron nano-particles were synthesized via the sol-gel method and characterized by Energy-Dispersive Spectroscopy (EDS), Dynamic Light Scattering (DLS), Fourier Transform Infrared Spectroscopy (FT-IR), and Field Emission Scanning Electron Microscopy (FE-SEM). The reactors were operated sequentially in three distinct phases: physicochemicals, biological, and bio-electrochemicals, with a direct current applied under flow-through conditions. The biological samples were stained with acridine orange (AO) and examined using CLSM. The hydraulic retention time (HRT) of each column was approximately 293 min (4.9 h), the effective working volume was 440 mL and the operating flow rate was 1.5 mL min ⁻ ¹. The Fe-FAC reactor demonstrated superior DOC removal, reducing concentrations from 3.61 ± 1.68 mg/L to 1.64 ± 1.34 mg/L, compared to the GAC column's reduction (4.26 ± 3.21 mg/L to 2.56 ± 1.08 mg/L). Flow cytometry (FCM) analysis revealed that Fe-GAC exhibited a lower event density than GAC at comparable dilution levels, suggesting a regulatory effect on microbial populations and biofilm development. In Phase I, both reactors demonstrated high DOC removal efficiencies. During phase II, removal efficiency declined in both systems. By Phase III, GAC exhibited a marked decline in performance, accompanied by the release of DOC, while Fe-GAC maintained a superior and more stable removal efficiency.