Electrochemical Treatment of the Antibiotic Sulfachloropyridazine: Kinetics, Reaction Pathways, and Toxicity Evolution

The electro-Fenton treatment of sulfachloropyridazine (SCP), a model for sulfonamide antibiotics that are widespread in waters, was performed using cells with a carbon-felt cathode and Pt or boron-doped diamond (BDD) anode, aiming to present an integral assessment of the kinetics, electrodegradation byproducts, and toxicity evolution. H₂O₂ electrogeneration in the presence of Fe²⁺ yielded ^•OH in the solution bulk, which acted concomitantly with ^•OH adsorbed at the anode (BDD­(^•OH)) to promote the oxidative degradation of SCP (<i>k</i>_abs,SCP = (1.58 ± 0.02) × 10⁹ M^–1 s^–1) and its byproducts. A detailed scheme for the complete mineralization was elucidated. On the basis of the action of ^•OH onto four different SCP sites, the pathways leading to total decontamination includes fifteen cyclic byproducts identified by HPLC and GC-MS, five aliphatic carboxylic acids, and a mixture of Cl^–, SO₄^2–, NH₄⁺, and NO₃^– that accounted for 90–100% of initial Cl, S, and N. The time course of byproducts was satisfactorily correlated with the toxicity profiles determined from inhibition of <i>Vibrio fischeri</i> luminescence. 3-Amino-6-chloropyridazine and <i>p</i>-benzoquinone were responsible for the increased toxicity during the first stages. Independent electrolyses revealed that their toxicity trends were close to those of SCP. The formation of the carboxylic acids involved a sharp toxicity decrease, thus ensuring overall detoxification

Regeneration of Activated Carbon Fiber by the Electro-Fenton Process

An electro-Fenton (EF) based technology using activated carbon (AC) fiber as cathode and BDD as anode has been investigated for both regeneration of AC and mineralization of organic pollutants. The large specific surface area and low intraparticle diffusion resistance of AC tissue resulted in high maximum adsorption capacity of phenol (PH) (3.7 mmol g^–1) and fast adsorption kinetics. Spent AC tissue was subsequently used as the cathode during the EF process. After 6 h of treatment at 300 mA, 70% of PH was removed from the AC surface. The effectiveness of the process is ascribed to (i) direct oxidation of adsorbed PH by generated hydroxyl radicals, (ii) continuous shift of adsorption equilibrium due to oxidation of organic compounds in the bulk, and (iii) local pH change leading to electrostatic repulsive interactions. Moreover, 91% of PH removed from AC was completely mineralized, thus avoiding adsorption of degradation byproducts and accumulation of toxic compounds such as benzoquinone. Morphological and chemical characteristics of AC were not affected due to the effect of cathodic polarization protection. AC tissue was successfully reused during 10 cycles of adsorption/regeneration with regeneration efficiency ranging from 65 to 78%, in accordance with the amount of PH removed from the AC surface