Dissolved Oxygen Changes in Wastewater During Sulfamethoxazole Degradation by Photo-Fenton Treatment

This study examines the degradation of sulfamethoxazole (SMX) in water using the photo-Fenton process, focusing on dissolved oxygen (DO) dynamics, organic matter mineralization, and water quality improvement. The results show that SMX degradation follows a rapid kinetic pattern, achieving complete removal within 30 min. However, total organic carbon reduction occurs more gradually, indicating the persistence of organic intermediates before full mineralization into CO 2 and H 2 O. DO evolution follows a biphasic trend: an initial decline due to oxidative consumption, followed by an increase due to H 2 O 2 decomposition into O 2 . Initially, at [H 2 O 2 ] 0 ≥ 3.0 mM, DO sharply increases, while at [Fe(II)] 0 = 5.0 mg/L, DO reaches a minimum of 0.3 mg/L due to higher reactive oxygen species (ROS) production. Water quality parameters such as color, turbidity, and aromaticity were also monitored. Aromaticity significantly decreases within 30 min, confirming SMX ring cleavage. Color and turbidity initially intensify and increase due to intermediate formation but later decrease as mineralization progresses. Optimal conditions (1 mol SMX: 10 mol H 2 O 2 : 0.05 mol Fe(II)) ensure efficient degradation with minimal oxygen depletion without excessive scavenging effects. These findings confirm that the photo-Fenton process effectively removes SMX while improving water quality, making it a sustainable alternative for pharmaceutical wastewater treatment.