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.

► The electro-Fenton process effectively enhanced the mineralization of metronidazole.
► The optimum conditions for the electro-Fenton process were identified.
► A comparative analysis of MNZ toxicity and biodegradability between the EF and EC was assessed.
► EF process increased the biodegradability and decreased the toxicity of MNZ wastewater.