Mineralization of erythromycin by UV-based and electro-oxidation processes

Antibiotic contamination is a relevant environmental problem, since these compounds are discharged in conventionally treated wastewaters, and can favor antibiotic resistance. In this work, the mineralization of solutions containing 50 mg/L of erythromycin, part of the European Union wide watch-list, was studied using electro-oxidation and the UV-based processes direct photolysis, heterogeneous photocatalysis and photo-electrocatalysis. For the UV-based processes, a higher photonic flux favored mineralization and lowered energy consumption, since it increases both molecule absorbance and hydroxyl radical production. For the high photonic flux experiments, direct photolysis presented higher mineralization (42%) than photocatalysis (16%), which might be explained by the reactor configuration, the electronic recombination and the erythromycin concentration. Electro-oxidation presented low overall mineralization (<10%), but had synergistic effects when combined to photocatalysis, resulting in 38% mineralization for photo-electrocatalysis. Matrix effects on mineralization were evaluated by performing photo-electrocatalysis and direct photolysis experiments with a spiked real wastewater. While direct photolysis resulted in no mineralization due to photochemically active light filtering by dissolved organic matter and inorganic ions, photo-electrocatalysis with the spiked wastewater did not differ significantly from photo-electrocatalysis with the working solution and would be a more viable alternative. The use of a supporting electrolyte for the photo-electrocatalysis experiments with spiked wastewater resulted in no significant difference in mineralization, but probably led to different reaction pathways, as suggested by chloride and nitrogen species concentration analysis.