Optimization of fipronil removal via electro-Fenton using a carbon cloth air-diffusion electrode

• Efficient production of H 2 O 2 using an undivided BDD/carbon cloth air-diffusion cell. • Hydroxyl radical at the BDD and in the medium as oxidants of fipronil by EF . • 85 % removal for 10 mg L −1 fipronil at 0.50 mM Fe 2+ , pH = 3.0, and 30 mA cm −2 . • Excellent reusability and stability of the system after 7 consecutive cycles. • Acetic, fumaric, formic, oxalic, and oxamic acids detected as final carboxylic acids . The electro-Fenton (EF) process using a boron-doped diamond (BDD) anode and a carbon cloth air-diffusion cathode was optimized for efficient fipronil degradation. The system achieved high H 2 O 2 electrogeneration with close to 80 % current efficiency operating between 10 and 50 mA cm −2 , with hydroxyl radicals formed from BDD oxidation and Fenton’s reaction that drive pollutant decay. Optimum conditions were found with 0.50 mM Fe 2+ catalyst at pH = 3.0 and 30 mA cm −2 , yielding almost complete removal for 20 mg L −1 fipronil in 60 min, 85 % removal for 10 mg L −1 , and a robust performance down to 1 mg L −1 , thus reflecting real-world applicability. The system demonstrated excellent reusability and stability over seven consecutive runs. The evolution of final short-chain linear carboxylic acids like acetic, fumaric, formic, oxalic, and oxamic, and inorganic ions like F − , Cl − , and NH 4 + , was determined. This study highlights the EF process as a highly efficient, energy-balanced, and stable solution for fipronil degradation in water treatment.