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Abstract Solutions of 200 mg L−1 cefalexin (CLX), an antibiotic with high usage frequency and biodegradation resistance, have been comparatively degraded by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes using two kinds of activated carbon fiber (ACF) cathodes with different physical properties. These two ACFs shared similar pore volumes and pore diameters but varied BET surface areas, which were confirmed to be 0.5210 cm3 g−1, 2.26 nm and 921 m2 g−1 for ACF1, while 0.6508 cm3 g−1, 2.16 nm and 1206 m2 g−1 for ACF2, respectively. Their oxidation abilities were comparatively assessed in terms of degradation kinetics and mineralization rates, which increased in the order: ACF1-EF < ACF2-EF < ACF1-PEF < ACF2-PEF. These results confirmed the superiority of ACF with higher surface area, which was correlated to faster H 2 O 2 and OH accumulation in more reaction sites provided. After 120 min electrolysis, ACF1 exhibited 1510 μM H 2 O 2 and 37 μM OH accumulation, while ACF2 generated 1934 μM H 2 O 2 and 85 μM OH. Moreover, ACF cathode with more developed pore structure also revealed faster formation of degradation by-products like inorganic ions (NH 4 + and NO 3 − ions) and short-chain carboxylic acids (acetic, formic, oxamic and oxalic acids), as well as enhanced removal for partial acids. In order to gain a deeper understanding of degradation mechanisms for ACF2-PEF system, evolutions of six aromatic by-products generated from sulfoxidation, hydroxylation and decarboxylation were confirmed by UPLC-QTOF-MS/MS determination. Based on the above identifications of the degradation intermediates, a plausible reaction pathway for CLX removal was proposed. Graphical abstract Image 1 Highlights • Cefalexin was degraded by EAOPs with varied surface properties ACF cathodes. • Faster decay and higher mineralization achieved by larger specific area cathode. • ACF with higher specific area could promote H 2 O 2 and OH production. • Quicker by-products formation and elimination attained in more porous ACF cathode. • 6 aromatic products were detected and a plausible reaction pathway was proposed. [ABSTRACT FROM AUTHOR]

This work investigated the effect of the chelation of Fe 3+ with a fluoroquinolone (FQ) antibiotic ciprofloxacin (CIP) on the catalytic behavior of Fe 3+ /Fe 2+ and the degradation and mineralization of CIP in electro-Fenton (EF) process using activated carbon fiber (ACF) felt cathode. First of all, effect of initial Fe 2+ and Fe 3+ concentrations on the degradation and mineralization of CIP in EF process was compared, while the optimal initial Fe 2+ and Fe 3+ contents were both verified to be 1.50 mmol dm −3 , in which 73% and 72% of initial TOC were eliminated after 360 min electrolysis, respectively. Secondly, Fe 3+ -CIP chelate was produced during CIP degradation in EF process, whose predominant form was confirmed as 1:2 metal-ligand stoichiometry. The formation of Fe 3+ -CIP chelate had no obvious inhibition on the degradation and mineralization of CIP due to the efficient Fe 3+ reduction on the ACF cathode with excellent catalytic feature. About 17% and 35% of initial 1.50 mmol dm −3 Fe 3+ were reduced to Fe 2+ at 18 mA cm −2 in ultrapure water and 200 mg dm −3 CIP solutions during 30 min pre-aeration of EF process, respectively, while higher Fe 2+ concentration was maintained for initial 1.50 mmol dm −3 Fe 3+ during CIP degradation. Finally, the evolution of F − , NH 4 + and NO 3 − ions released to the acidic medium were determined, as well as the formation of short-chain carboxylic acid (oxalic, oxamic and formic acids). Eight aromatic intermediates were identified using UPLC-QTOF-MS/MS, and a feasible mineralization pathway was proposed. [ABSTRACT FROM AUTHOR]

Solutions of 500 mL 200 mg L −1 fluoroquinolone antibiotic levofloxacin (LEVO) have been degraded by anodic oxidation (AO), AO with electrogenerated H 2 O 2 (AO–H 2 O 2 ) and electro-Fenton (EF) processes using an activated carbon fiber (ACF) felt cathode from the point view of not only LEVO disappearance and mineralization, but also biodegradability enhancement. The LEVO decay by EF process followed a pseudo-first-order reaction with an apparent rate constant of 2.37 × 10 −2 min −1 , which is much higher than that of AO or AO–H 2 O 2 processes. The LEVO mineralization also evidences the order EF > AO–H 2 O 2 > AO. The biodegradability (BOD 5 /COD) increased from 0 initially to 0.24, 0.09, and 0.03 for EF, AO–H 2 O 2 and AO processes after 360 min treatment, respectively. Effects of several parameters such as current density, initial pH and Fe 2+ concentration on the EF degradation have also been examined. Three carboxylic acids including oxalic, formic and acetic acid were detected, as well as the released inorganic ions NH 4 + , NO 3 − and F − . At last, an ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry was used to identify about eight aromatic intermediates formed in 60 min of EF treatment, and a plausible mineralization pathway for LEVO by EF treatment was proposed. [ABSTRACT FROM AUTHOR]