Synergistic oxidation and adsorption of humic acid by electro-activated ferrous: Process exploration, mechanism...

Conventional drinking water treatment processes exhibit limited efficiency in removing humic acid (HA), making it difficult to effectively suppress the formation risk of disinfection by-products (DBPs). To address this issue, an electrochemical pretreatment system integrating synergistic oxidation, flocculation, and co-precipitation processes was developed. This system employs electro-activated ferrous (EAF) to enhance HA removal and thereby mitigate the formation of DBPs precursors at the source. Using a Ti/TiO₂-Ta₂O₅-IrO₂ anode and a graphite cathode, under the conditions of 30 mg L^-1 Fe²⁺ dosage, 3 mA cm^-2 current density, and 2 cm electrode spacing, the removal rate of natural organic matter reached 92.62% ± 1.99%. Analysis via three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) and ultraviolet-visible absorption spectroscopy (UV-Vis) collectively confirmed that macromolecular HA underwent significant oxidative cleavage and adsorption removal in the reaction system. Hydroxyl radicals (·OH) attacking HA molecules were identified as the key mechanism driving oxidative degradation. Meanwhile, the continuous redox cycling of iron species (Fe²⁺/Fe³⁺) in the system facilitated this process, and the resulting Fe³⁺ effectively removed HA and their degradation products through flocculation. Furthermore, the coexistence of Fe, O, and C elements within the flocs, along with the identified coordination structures between HA and Fe(OH)₃, directly confirms the binding of organic matter, such as HA, onto iron hydroxide flocs. Finally, the applicability of this technology was validated in real water samples, and its disinfection efficacy was evaluated through microbial diversity analysis.