Goethite-activated carbon as a persulfate activator for effective Escherichia coli inactivation

In this work, α-FeOOH modified activated carbon (FeOOH@AC) was prepared through wetness-impregnation and used as a persulfate (S2O82−, PS) activator to inactivate Escherichia coli in water. Surficial analysis displayed that micron-sized (0.5 to 1 μm) goethite was evenly distributed on AC. The structural ferric ions in the FeOOH matrix were partially reduced to ferrous ions by the hydroxyl of AC. The surface-bonded Fe2+ facilitated PS to produce hydroxyl and sulfate radicals (·OH and SO4·−). These radicals effectively inactivated Escherichia coli by destructing bacterial membrane. Therefore, the FeOOH@AC-PS system obtained a higher inactivation rate of 6.0 log as compared to 3.1 log and 0.4 log in the AC-PS and FeOOH-PS systems, respectively. After sterilization, the Escherichia coli did not regrow in the FeOOH@AC-PS system within 48 h, indicating its persistent growth inhibition by radicals. The FeOOH@AC-PS system also showed high inactivation efficiency over a pH range of 3 to 11 and excellent stability in cyclic test. Spent FeOOH@AC was amenable for effective regeneration by eliminating surficial iron oxides with hydrochloric acid and reloading FeOOH through wetness-impregnation with a regeneration rate up to 96.7 %. These results demonstrated that FeOOH@AC can effectively and stably activate PS for inactivating bacteria in water.