Sustained persulfate activation using solid iron: Kinetics and application to ciprofloxacin degradation

Characterization of persulfate activation by solid iron was performed to determine kinetic parameters and control variables. The solid iron activated persulfate system was then used to demonstrate the degradation of the fluoroquinoline antibiotic ciprofloxacin. This study established the persulfate activation using solid iron takes place via a zero-order mechanism. Persulfate reaction rates were found to be linear functions of iron rod surface area, with a maximum reaction rate constant of 8.4 × 10−7 mol L−1 s−1 established at the highest iron rod surface area tested. Persulfate reaction rates increased with the current applied to an iron rod up to a current density of 8.2 mA cm−2 after which the rate plateaued. A maximum rate of 7.1 × 10−7 mol L−1 s−1 was established with applied current compared to 4.3 × 10−7 mol L−1 s−1 without current, when the same surface area of the iron rod was in solution. At a starting concentration of 0.121 mmol L−1, ciprofloxacin removal of 95% was achieved in 15 min. A ciprofloxacin transformation product matrix containing core quinolone structures was formed and then degraded by 90%, with total organic carbon removal of 44%. The corresponding defluorination was >95%, suggesting that solid iron activated persulfate may offer an advantage for destruction of some fluorinated compounds. Hydroxyl radicals were identified as the dominant radicals in the degradation process. Ciprofloxacin removal was independent of the applied current despite the increased persulfate activation under the same conditions.