Efficient removal of perfluoroalkyl acids (PFAAs) from aqueous solution by electrocoagulation using iron electrode

• PFAAs as emerging contaminants were effectively removed by electrocoagulation.
• Iron hydroxide flocs formed in situ presented high removal efficiency for PFAAs.
• The important factors included current density, stirring speed, and electrolyte type.
• More than 99% PFOS was removed after 50-min electrolysis with 25.0 mA/cm2.
• Further mechanistic detail of PFAA adsorptive removal on iron flocs is proposed.

Electrocoagulation (EC) technique was used to investigate the removal performance of aqueous perfluoroalkyl acids (PFAAs) with relatively high concentration as simulating the wastewater from organic fluorine industry. A comparison between iron and aluminum electrode was made to remove PFAAs with the similar electrolysis condition. Effective removal of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) was obtained by EC process, especially for Fe anode. Several key factors were studied to optimize the EC process using Fe electrode. At the optimal operating parameters including 25.0 mA/cm2 of current density, 180 rpm of stirring speed, and 2 g/L NaCl as supporting electrolyte, more than 99% of PFOS could be removed with 0.25 mM of initial concentration after 50-min electrolysis. Additionally, the adsorptive removal of aqueous PFOS on iron hydroxide flocs during EC was also verified by Fourier transform infrared spectra. The investigation of removal efficiency for PFAAs with different carbon chain length after EC and the characteristic of zeta potential on Fe flocs indicated that the electrostatic adsorption was primarily responsible for the PFAAs sorption on the iron hydroxide flocs.

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