Enhancement of mineralization of metronidazole by the electro-Fenton process with a Ce/SnO₂–Sb coated titanium anode

We compared the degradation behavior of metronidazole (MNZ) under advanced oxidation processes with the aim of enhancing the mineralization of MNZ. Among the advanced processes used, that is, Ce/SnO₂–Sb/Ti electrochemical/anode oxidation (EC/AO), the Fenton and the electro-Fenton (EF) processes, the EF process was the most effective. Different input variables, including catalyst concentration, [H₂O₂]/[Fe²⁺] molar ratio, and pH level were evaluated to find the optimum condition for mineralization by EF treatment. The total organic carbon was optimally diminished by up to 37% by applying a Fe2+ concentration of 2.0 mM, a [H₂O₂]/[Fe2+] molar ratio of 10:1, and a pH of 2.0. The change in biodegradation was investigated on the basis of the BOD₅/CODcr ratio. The ratio of BOD₅/CODcr of raw MNZ aqueous (0.227) was increased to 0.252 and 0.345 by the EC and EF systems, respectively. The general toxicity resulting from the different treatments for MNZ aqueous solution was assessed by the Photobacterium bioassay. The toxicity of the EF-treated solution decreased 63%, falling to an effectively non-toxic level, indicating that the EF process can decontaminate and mineralize MNZ into a non-toxic product. According to the BOD₅/CODcr ratio, the EF process is a sufficiently powerful pretreatment technology that can increase the biodegradability and decrease the toxicity of wastewater containing MNZ, providing a favorable condition for subsequent biochemical treatment. Copyright © 2013 Elsevier B.V. All rights reserved.