Enhancing the Fe3+/Fe2+ biocatalytic cycle using deoxidizing and iron-releasing sticks to improve bio-fenton efficiency

Abstract

Although microorganisms in bio-Fenton (BF) systems can produce hydrogen peroxide autonomously, reducing the demand for external H₂O₂ addition, Fe³⁺ accumulation, and the formation of iron sludge are persistent challenges. This study investigates the effects of iron-reducing bacteria (IRB) and deoxidizing and iron-releasing sticks (DIRS) on the Fe³⁺/Fe²⁺ cycle in a baffled bioreactor (BBR). Performance enhancements were evaluated using parameters such as dissolved oxygen levels, H₂O₂, hydroxyl radical (•OH) generation, and Fe³⁺/Fe²⁺ ratios in the system. Results indicated that the electrochemically active surface area of DIRS, measured by cyclic voltammetry (0.368 mA/cm²), was 92 times greater than that of conventional carbon cloth, with a charge transfer internal resistance of only 795 Ω—30.1 % of the carbon cloth's value. Surface analysis showed that DIRS had abundant functional groups and a higher carbon-to‑oxygen ratio. Compared to unmodified wool brushes, DIRS exhibited considerably enhanced microbial adhesion after experiments, leading to a 1.05–1.35-fold increase in H₂O₂ production. Furthermore, the Fe²⁺/Fe_total ratio improved from 17.4 % to 91 %. Notably, DIRS-enriched IRB such as Acidovorax, Pseudomonas, and Shewanella were identified, demonstrating their potential for in situ BF wastewater treatment applications. Therefore, the DIRS surface can be favorable for microorganisms to form biofilm and for Fe-reducing bacteria to become a dominant species.