Sulfamethoxazole abatement by photo-Fenton: Toxicity,inhibition and biodegradability assessment of intermediates

The objective of this work was to study the abatement of 200 mg L⁻¹ sulfamethoxazole (SMX) solution by means of photo-Fenton process. Biodegradability of the treated solutions was followed by the ratio biochemical oxygen demand at five days/chemical oxygen demand (BOD₅/COD) and toxicity by Microtox^® and inhibition tests. Experiments with different initial concentration of H₂O₂ were carried out. The initial amount of Fe²⁺ and pH of the solution were set at 10 mg L⁻¹ and 2.8 respectively. The temperature of the reactor was kept constant in all the experiments (25 ± 0.8 °C). Photo-Fenton process is thought to be a successful treatment step to improve the biodegradability of wastewater containing SMX. The complete antibiotic removal was achieved for a H₂O₂ dose over 300 mg L⁻¹. Biodegradability (BOD₅/COD) rose from zero (SMX solution) to values higher than 0.3 (treated solutions). Toxicity and inhibition tests pointed out in the same direction: oxidized intermediates for initial H₂O₂ dose over 300 mg L⁻¹ showed no toxicity effects on pure bacteria and no inhibition on activated sludge activity.